L. PHYSICAL GEOGRAPHY. CLIMATOLOGY
WEATHER, CLIMATE, AND TEMPERATURE—ISOTHERMAL LINES—ISOBARS, WEATHER FORECASTS, AND SIGNS OF THE SKY.
It is usually considered a sign of a paucity of ideas when one begins a conversation about the “weather,” but there can be no doubt that there is no more interesting question in social life at certain times as to whether it will or will not rain. Our outdoor amusements are all dependent upon weather, and a little cloud may throw a deep shadow over all our pleasure if we neglect to bring out an umbrella, or to carry a waterproof. We are never independent of what we term the “capricious” climate, but in reality the laws of “the Weather,” though so imperfectly understood, are fixed and invariable, and if we could read the signs in the sky and learn the condition of the atmosphere, we might leave the “prayers for rain” and “for fine weather” out of the Church service, for then we should understand that unless miracles are performed for us the laws of Nature can in no wise be altered.
Of late years weather forecasts (not prophecies) have come before us in our newspapers after the manner instituted by the late Admiral Fitzroy, whose name has become a household word in England. But at the commencement of the Christian era and before that time the signs of the heavens and the behaviour of animals and birds were noted with reference to changes of weather. If we read Virgil we shall find numerous references to these portents, and the translation usually quoted will furnish us with information which must be as true nowadays as it was in Virgil’s time, for wild animals do not change their habits. Speaking of wet weather in the Georgics the poet wrote:—
“The wary crane foresees it first, and sails Above the storm, and leaves the hollow vales; The cow looks up, and from afar can find The change of heaven, and sniffs it in the wind; The swallow skims the river’s watery face, The frogs renew the croaks of their loquacious race; The careful ant her secret cell forsakes, And draws her eggs along the narrow tracks; Huge flocks of rising rooks forsake their food, And, crying, seek the shelter of the wood.
* * * * *
The owls, that mark the setting sun, declare A starlight evening and a morning fair.”
We might quote further selections respecting the signs in the heaven and earth mentioned, but the foregoing verses will be sufficient to illustrate our position, and to show us that weather forecasting is, at any rate, as old as the Christian era.
The moon is generally supposed to influence the weather—a “Saturday’s Moon” being particularly objectionable, or when she appears anew at some hours after midnight thus—
“When first the moon appears, if then she shrouds Her silver crescent, tipped with sable clouds, Conclude she bodes a tempest on the main, And brews for fields impetuous floods of rain.”
Weather permitting, we can go out and study the clouds as described in the foregoing chapters, or consult the barometer, and see which way the wind blows. The child will tell us that a high “glass” means fine weather, and a low barometer indicates rain, but this is only relatively true. A high glass may be falling, a low glass may be rising. A sudden fall or a sudden rise are indicative of bad, windy weather, or a short-lived fine period. The glass may rise with a northerly wind, and rain will supervene, so careful observation is necessary before one can obtain even a superficial knowledge of the weather. (See subsequent observations on “Weather.”)
The Americans telegraph the results of their observations of coming storms across the Continent, corrected by the signs noticed and recorded by vessels arriving in New York. Thus they are frequently very accurate; steady application and observation at Sandy Hook must give them a great deal of useful information for the “forecasts.”
The word CLIMATE is derived from the Greek klima, a slope; and thus at a glance we perceive how the aspect it presents to the rays of the sun in the earth’s revolutions, must affect the “climate” of a country. Of course the position of any portion, the elevation and locality of the mountains, have also a share with the soil, winds, rains, and sea-board, in determining the climate of any region. Many points have already been touched upon in former chapters. Temperature, moisture, and vegetation are the chief natural features which determine climate, and we must find out the position of the land with reference to the sun first, to ascertain the climate.
The more vertical the sun is the hotter the atmosphere, for the rays strike directly upon the earth, which radiates the warmth received. These heat rays are, as we know, invisible. The hottest portion of the earth must be at the equator for the sun is overhead, and the rays beat down directly upon the earth. The sun is also nearer than when at the horizon, and less rays are absorbed by the atmosphere. The longer the day the greater the heat.
Temperature is registered by observation of the thermometer, and the distribution of heat is represented upon a chart across which lines are drawn at places of equal temperature. These lines are called “isothermal.” There are also terms to denote equal winter temperature and the average summer heat—isochimines and isotheres respectively.
Temperature decreases as we ascend from, and increases as we descend into, the earth. This fact proves that the air is not warmed by the sun’s heat, but by radiation from the ground. As we ascend we reach the line of perpetual snow, which varies in different parts of the globe. In the tropics it extends from 15,000 to 18,000 feet; but it varies even in places of the same latitude, according as the towns are inland or on the coast, as in the Pyrenees and Caucasus, where there is a difference of three thousand feet in the snow limit.
The line of the snow limit, as a rule, gets lower as we journey from the equator to the poles. Exception will be found in the Himâlaya, where the snow line is higher on the northern side, in consequence of the existence of the Thibetan tableland, which causes a higher temperature than that existing upon the abrupt southern slope. Countries, therefore, though in the same latitude, may have different climates according to the elevation of the land.
The proximity to the sea is another reason for climatic difference. Water takes some time to become warm, but when it has once become so it will not readily part with its heat. The Gulf Stream, with its warm current beating along our shores, gives us a high temperature and a moist climate—a very different condition to Newfoundland or Nova Scotia, which are in much the same latitude as England and Ireland. By the sea the climate is more uniform, and the extremes of heat and cold are not so distant. We send invalids to the seaside to save them the effects of such violent changes. Winters are milder and summers cooler by the sea.
We can readily understand how such circumstances affect the vegetation, and places which in winter may enjoy a mild and genial climate (comparatively speaking), may have a cold summer. Ferns may flourish in winter out of doors, but wheat will not ripen in the autumn owing to the want of heat.
The winds also, and the soil and aspect of a region, all have a share in determining its climate. Trees bring rain by evaporation, and a wooded country is a blessing to its inhabitants, defending their habitations from wind and avalanches in mountainous districts. But the climatic conditions are altering. The ground is being more and more cleared; the soil is more cultivated, and moisture is being more eliminated from it. Therefore the air becomes warmer by the radiation of the ground, and clouds are formed which keep the warm layers down nearer the earth. Mountains, as we have seen, affect the rain-fall in districts; and in Scandinavia—in Norway chiefly—the average rain-fall is very high. The sheltering effects of mountains from east or northerly winds also alter the climate, while clay or gravel soils are cold or warm inasmuch as they absorb, or evaporate, moisture. Some surfaces being different from others give out more heat.
In some mountainous districts we shall find every variety of climate from the sea-level tropical heat to the rigours of the pole. The greatest average temperature is north of the equator in Africa; the lowest in the north, to the west of Greenland. Masses of land act in a different manner to the oceans, and the former become heated and cooled with equal rapidity, while the sea, as already mentioned, is slow to lose its heat. Our land enjoys a mild and equable climate as a rule, because it is surrounded by water, and the Gulf Stream warms it. The European climate, taken altogether, may be considered the best on the globe.
We will now pass on to a few observations concerning the weather, and the means of determining it beforehand.
It is always a dangerous thing to act the part of a prophet, and the uncertainty attending an uninspired foreteller’s predictions must in time disparage him in the estimation of his hearers and disciples. But there are signs in the sky which we can discern and render valuable by the aid of instruments. We must have a reliable barometer and thermometer, and keep a record of the average conditions of the weather, if we wish to wear the mantle of the weather-prophet—a term now, in America, applied (jokingly, no doubt) to people who are not particular in their statements of facts.
But without entering upon any scientific discussion, we may state a few plain rules which can be observed, besides the indications of a rising or falling barometer. Having frequently studied the aspects of the clouds, with the assistance of the hints from the wind-currents, we can fairly prognosticate or suggest probable changes of weather.
We have already remarked upon the colours of the sunset, which are attributable to the vapours in the atmosphere, and we say a red sky foretells fine weather; a yellow sky changing into green means rain, or rain and wind; on the other hand, when the red rays appear we may anticipate fine weather, as the atmosphere is becoming less and less moist.
A “low” dawn is known as a good sign; so when the first rays appear at, or near the horizon, we may anticipate a fine day, as we may when the morning is grey.
“Evening red and morning grey”
are almost unfailing tokens of fine weather.
Very often a yellow sunset means wind; a wild, crimson sky means a gale. On the afternoon (Saturday) before the Eurydice foundered off the Isle of Wight, we particularly noted the sunset at Gravesend; and it was evident (in our estimation) that a sudden storm was imminent, and we remarked it to our companions. The sudden fall of the barometer, and the appearance of the rising clouds early on that sad Sunday afternoon, approaching in dark masses from the west and north-west, spoke of rain and (possibly) snow. How true the forecast was the event proved.
When clouds are soft and thin we expect fine weather; when they are dark and hard, rain and wind. A ragged-edged and heavy cloud indicates thunder and lightning, with squalls when we see dark clouds flying rapidly across the mass of cumuli. A “mackerel” sky and “mares’ tails” generally foretell wind, the direction and the upper currents being noted. The longer the warning given by the heavens, the longer the bad (or fine) weather will last; and the converse is also true.
“Evening grey and morning red, Put on your hat, you’ll wet your head.”
The cirrus is a wispy cloud, and is often observed extending across the sky on a fine afternoon. This may or may not indicate rain; it generally points to wind. If its direction be northerly and west to southerly and east, it is a good sign, but from west to east it is a bad sign. The habits of birds and animals, and their anxiety for shelter, “pigs running with pieces of straw in their mouths,” and the low-flying swallow, are all signs of approaching rain and bad weather, and the scintillation of stars betokens moisture in the atmosphere. These are well-known appearances, but there are others regarding the winds and currents of air which require the assistance of Admiral Fitzroy’s book.
For instance, a falling barometer with rising temperature means southerly winds and rain; in winter, with low temperature, snow.
But a rising barometer with northerly wind often means rain.
A rising glass after a low fall may, and often does, indicate more wind from the north, and after that fine weather, if lower temperature also supervene. If warm weather continue under the circumstances, the wind may back and blow from the southward.
“The most dangerous shifts of wind happen soon after the barometer rises from a very low point, or if the wind veers gradually shortly after with a rising barometer.”
If the barometer rises with a southerly wind fine weather may be expected, and if it falls with a northerly wind rain, hail, and snow are imminent, for the rule is a fall for southerly, and a rise for northerly winds.
A sudden fall with west wind indicates storm from northerly quarters (N.E. to N.W.). An east gale veering southwards with falling glass indicates a change of storm-direction to a point from N.W. or N.E., suddenly and violently, though a change might have been expected from the appearance of the glass. A calm frequently occurs between these disturbances.
A backing wind—that is, a wind going in a direction opposed to the sun’s course (and with the earth)—is a bad sign after unsettled weather. The wind is said to “veer” when it goes with the sun.
The south-east wind, with clear sky, warm weather, and low clouds on the horizon, is a sign of wet. A dry east wind means fine weather. Heavy clouds in the north-west generally bring a thunderstorm. When really distant objects look very near rain must be expected.
There are many exceptions to weather rules, and none can be laid down as invariable. The ever-changing currents of air, and varying moisture of the atmosphere, give rise to barometric changes, which should be carefully noted. A little experience and close observation for one year, with notes of signs, and indications of temperature, will assist any one to tell the probable change that is approaching.
There are a great number of signs of weather which are observable in the animal and even in the vegetable kingdom, as well as in the moon and stars. Many flowers close their petals before rain comes on, and the behaviour of domestic animals often foretells storm. Sheep huddling together in a corner tell us the direction from which the tempest is approaching; sea birds fly to shore, and land birds become restless.
The naturalist will observe the domestic animals which become uncomfortable and sniff the air; the cat lies with her head down, the brain lowest; and frequently washes her face, or scampers about aimlessly. Spiders disappear, and worms come up to seek the expected water. When fine weather is coming all nature appears glad, but leeches sink into the water as far as they can.
The above are some of the domestic and common signs of coming rain, and conversely for fine weather. A wailing wind, a cloudy mountain, a greenish rainbow or too red a one, a pale moon with indistinct points, or a halo round it, are all signs of rain and possibly wind. So the most superficial observer may with these few suggestions inform himself of the chances of fine or wet weather.
LI. BIOLOGY. PART I. BOTANY
PLANTS AND ANIMALS—STRUCTURE OF PLANTS—FLOWERING PLANTS—THE STEM—THE LEAVES—FORMS OF LEAVES.
BIOLOGY is derived from the Greek word Bios, “life,” and logein, “to speak,” and constitutes the science of ORGANIC LIFE. This science is divided into two branches: BOTANY, relating to the life of plants; ZOOLOGY, to the animals.
Plants, then, are living things, and as we proceed we shall find them born, or “germinating,” growing up as young plants, maturing as adults, and finally dying, and their particles resolving into their elements. There is more than one application of the text, “Man is but as a flower of the field.”
In the GEOLOGICAL section we noticed the progressive stages of the vegetable creation, and if we turn back to those pages wherein the various epochs of the earth’s formation are enumerated, we shall see how plant-life developed. Thus we find in the Cambrian the first traces of vegetable life in the weeds of primeval seas. The Silurian strata and the Devonian furnish us with many fossils of marine algæ, and if we examine the succeeding periods we shall find a progressive increase and development; pines and tree-ferns in the sandstone, and most of the plants (by which term we include all varieties) were different from those at present existing in the earth.
We spoke of climate lately, and referred to the vegetation having an influence upon it. The same is true of the effect of climate upon vegetation. The conditions of plant-life depend upon climate, as it partly depends upon plant-life. But of all the necessary conditions the first created thing is the most necessary—light. Without light the plant is nothing.
Plants have many points of similarity with animals. They live, they possess organs, their compositions contain similar substances, such as carbon and albumen, and close chemical analyses have found the existence of the elements oxygen, nitrogen, hydrogen, and carbon in animals and plants. Therefore water must play a conspicuous part in all. Professor Huxley puts this question in his usual clear fashion. He says:—
“It is a very remarkable fact that not only are such substances as albumen, gluten, fibrin, and syntonin known exclusively as products of animal and vegetable bodies, but that every animal and every plant at all periods of its existence contains one or other of them, though in other respects the composition of living bodies may vary indefinitely. Thus some plants contain neither starch nor cellulose, though these substances are found in some animals; while many animals contain no horny matter and no gelatine-yielding substance. So that the matter which appears to be the essential foundation of both the animal and the plant, is the proteid united with water, though it is probable that in all animals and plants these are associated with more or less fatty and amyloid (starchy and saccharine) substances, and with very small quantities of certain mineral bodies, of which the most important appear to be phosphorus, iron, lime, and potash. Thus there is a substance composed of water, plus proteids, plus fat, plus amyloids, plus mineral matters, which are found in all animals and plants. When these are alive this substance is termed PROTOPLASM.”
We have taken the liberty to extract the above paragraph, as it expresses in a few words, and very clearly, the common origin of plants and animals. We will now consider the conditions of plant life. Heat, light, and moisture are the principal necessaries, with of course air and certain earthy matter. Some plants, like some few animals, live in darkness, such as truffles and fungi, as do cave-fish and bats. But this is the exception, and the sense in which plants (or animals) can exist without light is a very restricted one, and only to be sustained at the expense of the plant material, which must originally have been derived by the action of light. Light, therefore, is the great “producer.” It gives life to plants upon which animals feed, and therefore light is in one sense the beginning of all things. We can now understand why light must have been created first.
Many interesting experiments can be made to observe the effect of darkness and different coloured light (transmitted through coloured glasses) upon plants; and it will be observed that although the leaves may not develop the natural green tint, the flowers will exhibit their usual colour. One effect of light upon plants is to make them green.
We all admire the beautiful green of the spring leaves, and the freshness of the colours of the trees and grass. But if we pluck up a plant its root is not green. Why then is the cleaned root not as green as the upper portion?—Because of the absence of light. There is a substance called Chlorophyl which, when acted upon by light, becomes green. This is contained in plants, and when the daylight falls upon it the substance turns green. So, as we said above, plants are not green when kept in the dark. Celery is a common instance. Heat, of course, has much to do with the activity or vitality of plants, and the range extends from just above freezing point to 122° Fahr. We find tiny plants blossoming in Alpine regions close to the snow, and others in full life in the tropics, protected from the fierce rays by scaly coverings and huge leaves. In the northern regions buds appear as soon as the surface warmth is felt, and even when no heat can yet penetrate to the roots. Thus we see that Nature fits the animal and the plant to the localities in which they live, and they exist interdependently. Some can defy cold, others flourish in drought; some love moisture, others live in great heat encased in prickly armour.
With this introduction to biology we may now pass on to speak of the seeds and germination of plants, which we divide into the flowering and non-flowering species. We suppose that the appearance of various organs of plants are familiar to our readers, and the root, the stem, the leaves, and the flower itself, as well as the seeds, are well known, and their uses understood generally.
Now if we compare a mineral—say a crystal of quartz—with a plant, we find the crystal uniform, consisting of small particles of quartz throughout, and it appears an aggregation from outside of these particles in a particular form. It cannot grow from within. But a plant can; and it is very different in structure and appearance. It receives nourishment from outside also, but it assimilates the materials, which are not the same as those we meet with in the plant itself. The mineral, on the contrary, is essentially the same throughout; it can only grow by aggregation of atoms like itself. A plant, therefore, like an animal, must have organs within it, and must be capable of change in itself; it has powers of reproduction, and in some few instances of locomotion; it can eat flies, and assimilate them as an animal does.
A plant, therefore, is an organized body without external voluntary movement; and hereby it is essentially distinct from an animal, with which, in organization, it is closely connected. The simplest form of the animal as of the plant, is that of a minute vesicle or cell, containing a fluid in which are some granular substances. At this stage it could not be distinguished from the simplest plant, if it had not the faculty of voluntary movement—the power of changing its place. The animal has a locomotive power. Sometimes, indeed, it is a very limited sphere to which it is confined; yet it may change its place for another more conducive to the exigencies of its being.
It is sufficient for the present to have given the most general characteristics by which plants are distinguished from the other objects that, with them, compose the great kingdom of Nature. A precise and clear apprehension of their varied forms and wonderful phenomena can only be obtained by a careful analysis of the nature and structure of the subjects of the vegetable kingdom.
The cell is the fundamental or elementary organ of plants, and the knowledge of its metamorphoses and functions constitutes the foundation of botany. We must therefore first consider the simple organs of plants.
STRUCTURE OF PLANTS.
It will be necessary for the reader to gain some little knowledge of the tissues and cells of plants before he proceeds to examine the organs of development, and a microscopic examination will soon disclose the few simple tissues which are termed cells and vessels. These exist in all plants of whatever nature. Plants are aggregations of cells, “every one of which has its little particle of protoplasm enclosed by a casing of the substance called cellulose, a non-nitrogenous substance nearly allied in chemical composition to starch.”[35] The tissues are “cellular” and “vascular” respectively.
The cells have an outer sac or covering which is transparent, and this cover is the cellulose above mentioned. It contains (1) the protoplasm, a kind of jelly-like substance (which holds the proteine or basis of life); (2) water or cell-sap; (3) the nucleus; and (4) chlorophyl. This protoplasm is apparent in both plants and animals. The cells containing these various substances—in which we find oxygen, hydrogen, nitrogen, sulphur, and carbon, with phosphorus perhaps—are divided to form new cells, and so on with most astonishing rapidity, amounting in some instances to millions in a day, and a case of this nature will readily be recognized in the mushroom.
Cellular tissue is composed of these cells, and vascular tissue is composed of vessels or tubes like coiled springs, which are cells without divisions or partitions. These tissues will be referred to farther on as dotted ducts or tubes.
In most of the spongy parts of plants, as in the pulp of fruits and pith of elder, the cells preserve the globular or oval shape represented in fig. 739 A. But the cells, in consequence of that mutual pressure, more frequently assume the form of a polygon (fig. 739 B), the section of which is generally hexagonal. The cellular tissue may generally be compared to the bubbles produced by blowing through a straw or tobacco-pipe into soap and water; or it may be illustrated by placing balls of moist clay together, and then pressing them more or less strongly. In this manner every individual ball assumes a polygonal shape corresponding to the form of the cells represented in fig. 739 C, and which disposition is, in many plants, preserved with the utmost regularity. Such cells as are, with tolerable equality, extended in all directions, are named parenchyma, and of these are composed the tuberous parts of plants, as the potato, dahlia-roots, etc., and especially the soft, spongy parts of the pith, bark, leaves, etc. We frequently, however, meet with cells which are extended longitudinally, and pointed at both extremities, as in fig. 740. The sections of these cells, which are compactly arranged, have the appearance of a hexagon. They are termed woody cells, or woody tissue (prosenchyma), and constitute the chief portions of the more solid parts of plants, as the ligneous parts of trees, shrubs, etc. Very long, flexible cells, as those which constitute the fibres of flax and hemp, are called bast-cells, and appear under the microscope as round threads of uniform thickness, whereas the fibres of cotton wool, which rarely exceed one or two inches in length, when magnified, present the appearance of flattish bands with somewhat rounded margins. By these marks, the union of flax and cotton in the same web or piece of cloth may be detected.
Occasionally the cells assume very abnormal shapes, as the stellate or star-formed cells. These are described as irregular cells.
As every plant, whether small or great, is only an aggregate of a great number of cells, so, also, the life of a plant is nothing else but the sum of the activities of all the cells of which it is composed. The special province of the cells is to receive from the soil or atmosphere the water necessary for the various vegetative purposes, together with the nutritious materials dissolved in the watery and aerial fluids, and to circulate them through the whole body of the plant. The circulation within a plant is not carried on through the agency of tubular channels, but only by the passage of sap in all directions from one cell to another.
Since the cells have no openings, it is somewhat difficult to understand in what manner the fluid can enter into the plant from without, and by what means it can inwardly pass from cell to cell. This phenomenon, however, is dependent on the peculiar quality both of vegetable and animal membranes and fibres—viz., that they are permeable by many fluids, without being dissolved by them. Experiments show that this permeative action is carried on in accordance with definite laws. When two fluids of unequal densities—as, for example, an aqueous solution of sugar and mere water—are separated from each other by a diaphragm of pig’s bladder, we perceive a constant tendency on both sides to restore the equilibrium in the density of the two fluids. A portion of the water penetrates the bladder, mixing with the solution, and a portion of the latter finds its way to the former by the same medium. In this experiment one important fact is to be observed—viz., that the lighter fluid always passes through the separating medium more rapidly to the denser than vice versâ; consequently, in this experiment more of the water passes through the bladder to the saccharine solution than of the latter to the water. This permeative capability of the tissue of vegetables and animals is called endosmose.
The cells both circulate the sap and alter its condition, so we find differing substances in the same plant. The cell as described creates new cells, and the force with which the sap rises is rather greater than the pressure of the atmosphere.
The vascular, or fibrous tissues, are illustrated in the margin (fig. 741). They usually contain air. Some plants have no vascular tissue, and are termed cellular plants—such as mushrooms, fungi, mosses, and seaweeds. Many contain both tissues, and these are the more highly developed kinds.
Sometimes we find a milky juice in plants. This is called latex; and caoutchouc is always present in it. This juice is contained in tiny tubular vessels, which have their origin in the new cellular tissue of the lactiferous plants.
The tissue of the cuticle, or epidermis, which externally covers all parts of the plant while they remain green, is of a peculiar nature, and demands special consideration. It is formed of flat tubular cells, very much compressed, and in close contact, with the exception of some parts where the stomata, or mouths, are placed. In fig. 742 a section of the leaf is represented, the large transparent empty cells of the epidermis, and above these the parenchymatous cells of the leaf filled with greenish-coloured granules. In four places (fig. 743) stomata (s s s s) are seen, which have their openings surrounded by parenchymatous cells disposed in semilunar forms. Under each stoma (mouth) there is a hollow space which is connected with the intercellular passages of the leaf. These stomata, represented in fig. 743, are so numerous on the under side of the leaf, that hundreds have been counted in the space of a square line. Through these minute organs an intimate connection exists between the interior of the plant and the external air.
The epidermal cells not unfrequently exhibit very abnormal formations. When much extended in length they appear as hairs which are frequently branched, and in many plants they contain an irritating sap (in the nettle, for example). Bristles, prickles, glands, warts, and especially the substance which forms the well-known cork, are all due to the metamorphosis of this exterior integument.
FLOWERING PLANTS.
Flowering plants have certain distinct features which cannot be mistaken, for they grow well above ground, and can easily be examined. There are a hundred-thousand different species of flowering plants, and a visitor to Kew can study them there. Any child can tell a flower when he sees it, but a flowering plant is no more restricted in BOTANY to actual bright blossoming plants, than the term rock in GEOLOGY means a mass of stone only. Flowering plants may be either very gorgeous or very simple; and so long as they contain a reproductive apparatus they are flowering plants. The rose is a flowering plant, but the oak is equally one. The beech tree and the primrose are classed under the same heading.
Flowering plants must possess stamens and pistils, which bring forth seeds which contain an embryo, and the germination of seeds can be easily perceived by any one who will take the trouble to soak them (say “scarlet runners”) in warm water, and keep them warm in moist flannel. The process may then be examined at leisure.
We need hardly insist, after what we have said, upon the necessity for some air and light, or remind the reader that he must not keep the seeds in a close, dark place, though light is not so necessary at first as air. The embryo connects the “cotyledons” or halves of the seed, and this develops into a tiny rootlet or “radicle,” and upwards into the stem, the commencement of which is known in botany as a “plumule.” The rootlet seeks nourishment from the ground. The albumen secreted in the cotyledons feeds the embryo, until (in some cases) it is exhausted and they die away. In other cases they grow up and obtain food for the young plant in the air. Some plants have (like wheat) only one seed-leaf, or cotyledon; and these kinds are called monocotyledons, or endogens, in which the growth is upright. The others are called dicotyledons, or exogens.
So far now, perhaps, you may understand that the outer covering of the seed is called the testa; the opening which may be perceived in the ordinary bean near the dark spot is the micropyle, or little gate; that the halves of the covering are termed cotyledons, or cups, and that the embryo sprouts upwards and downwards, the upper part of the stem being the plumule, and the lower portion the radicle. Even if the seed be put micropyle upwards into the ground, or between layers of flannel, to germinate, you will find that the radicle will always curve downwards.
The root then being displayed, it pushes its way into the ground to seek for nourishment, and when the proper moisture has been admitted to the seedling, which has been reposing in the cotyledons all the time, it sprouts up rapidly. The root and its fibrous extremities have been pushing and insinuating themselves into and through the ground, and by small knobs or suckers known as spongioles, the rootlets or fibrous parts of the root pick up sustenance for the plant, and it is then carried by tubes to the root, and so on throughout the plant, and with air ducts serve to keep the plant alive.
The stem emanates from the plumule, and in a short time little knots develop upon it, which are the incipient leaves. The knots are divided into nodes and internodes, because they appear on different sides of the stem and intermediate, so as to alternate with each other, and are really buds. The issues unite also into leaf-stalks or petioles, and extend into the leaf-frame or skeleton as we see it when the leaf has decayed. So thus we have an upward and a descending growth, which respectively constitute the stem and root of a flowering plant.
Some trees have roots growing from the stem, as in the banyan tree, and roots can produce stems as well as the latter can form roots. The uses of roots are so well understood that we need not particularize them. In many trees we find what are termed lenticellæ, like holes in the bark. These fissures will put forth roots under favourable circumstances. These stem roots are called adventitious, and by taking “cuttings” from plants we make good use of them for propagation.
But there are underground stems as well as those which flourish and climb above it. “Bulbs” and “tubers” are common instances of these underground stems, or “rhizoma,” which are horizontal. The ordinary stems are termed “aerial” stems to distinguish them from the earthy and subterranean. The aerial roots of ivy are only used for support, and are not its proper roots, though some parasitic plants strike into the trees and are nourished by them.
THE STEM.
The stem is that portion of the plant-axis which grows upwards or above ground, and may be, as we have just read, subterranean. As the great function of the root is to procure sustenance for the plant, the stem assists in carrying the nourishment through the branches and leaves. We shall find two forms of stem—the underground, or root-stock, and the stem proper. There are in these two former several varieties as under:—
1. The BULB, which is a short globular stem surrounded by thick leaves, and producing buds—as, for example, the onion.
2. The TUBER, similar to the foregoing in shape, having no leaves, however; the potato is an instance.
3. The RHIZOME (root-stock), like a root only producing buds, which roots do not. The iris will serve as an example.
The varieties of the stem-proper are:—
(1) Filiform, or thread-like, simple, or branched, as in mosses.
(2) The culno, a thin, hollow, and frequently-jointed stem.
(3) The palm or simple stem, seen in tree-ferns and palms. It is marked by the scars of dropped leaves.
(4) The stalk, very common, of a green hue, and its life is limited to a twelve-month as a rule. The so-called “stem” of the hyacinth is not a stem, it is a stalk, or flower-stalk, pushed forth for a temporary purpose.
(5) The ligneous stem is the perfected kind, and an example will be apparent in every tree.
The duration of the stem of a plant is usually the same as of the plant—so we have annuals, biennials, and perennials. The substance of the stem determines its character, so we may have it solid, or soft, hollow, tubular, flexible, rigid, or a tough stem. There are fibrous, herbaceous, and juicy stems. They may be directed uprightly, straight, procumbently, arched, or creeping, above, or underground, climbing, clinging, floating, or twining.
There are many plants with little or no stem deserving the name, as in the onion; and we must all remember when studying botany that it is not the place where a portion of a plant may be found that constitutes it a root or a stem. The form and structure should be studied, and its purpose in creation. So stems may be underground and roots above it. The root and stem, briefly treated of in the foregoing paragraphs, have certain points of resemblance, inasmuch as both consist of a main or trunk line, so to speak, from which branches diverge as “rootlets” and “twigs”; and how beautiful the latter are any one can see in a good photograph of a wintry landscape. But stems have nodes and internodes, and roots have not, and this is the great and apparent difference.
The covering of plant-stems is varied, and many instances of such clothing will occur. We have woolly stems and hairy stems, which develop into thorny ones—for thorns are only strong hairs. Spines and stings and prickles defend the stems, and keep rude hands from meddling. We will now cut the stem and see what it is composed of, and how it looks inside. We have only to cut it across and again perpendicularly to find out a great deal about the interior structure of the stems of branching plants (exogens).
The elder, from which the whistle of our boyish days is fashioned with a penknife, will serve any lad for an illustration. Inside we find what is called “pith,” which is cellular tissue. Round this is fibre, and outside is a skin, or the plant-cuticle. We may remark that the tissues of flowering plants are characteristic of the monocotyledonous and the dicotyledonous plants. Of the former we append an illustration,—a section of palm-stem,—and we find bundles of vascular tissue dispersed apparently at random amongst the cellular tissue of the parenchyma, or cellular tissue. These stems do not grow by the increase of the existing vascular tissue, but by their new production at the circumference, and so they grow in both directions, laterally and uprightly. These plants belong to the ENDOGENS, and if Indian corn be grown we shall have full opportunity to study the formation. In cutting a fern stem we are familiar with the “oak” pattern of the matter it contains. We have few specimens of endogens in England.
The dicotyledonous stems are common to our trees and most plants, and may therefore be considered with advantage. The stem consists of the vascular tissue called “pith,” and we give an illustration of the cells magnified very considerably. The arrow indicates the outward direction (fig. 757).
We here perceive the vascular bundle proper surrounded by a very large-celled tissue, aa′bef. The almost square cells, aa′ , form the epidermis on which follows the less dense cellular tissue of the bark. The latter surrounds a half-moon-shaped bundle of bast-cells, c, which are separated in the direction towards the interior, by a layer of cambium, dd′d″, from the bundles of vascular tissue, consisting of vessels and longitudinal cells. The latter tissues may be distinguished in the transverse section by the thicker walls, gg, and by their greater breadth, hh. It is further to be remarked that the cambium transparent tissue, dd″, appears on both sides of the bundles of vascular tissue, and extends to the next bundle, and thus presents an uninterrupted circle throughout the entire circumference of the stem.
On examining the section of a one-year-old dicotyledonous stem, magnified six times, as in fig. 758, we perceive several parts clearly distinguishable from each other, corresponding with the arrangement of the bundles of vascular tissue.
Enclosed by the epidermis, a, is a large-celled tissue, b f and m, in which a number of vascular bundles form a circle. In each of these we notice that the outer portion, consisting of bast-shell, c, is separated by the cambium, d, from the inner woody portion, e. The cambium forms a closed circle which penetrates through all the vascular bundles.
In the course of the further development of the stem, the parts, a b c, constitute the bark, the vascular bundles, e, the wood, and the cellular tissue, f, its pith. The tissues, m, penetrating between the vascular bundles, are called the medullary rays. The cambium is to be regarded as the most important part, since it is the source of new bundles of vascular tissue which year by year increase the circumference of the stem.
The growth of a dicotyledonous stem is continued by the formation of a new circle of vascular bundles on the circumference of the stem in the second year. Each new bundle, as has already been shown, is produced in the cambium, and consequently is deposited between the wood and inner bark.
Thus every year a new layer is deposited between the previous formation and the bark; and a section will exhibit these concentric rings of wood obviously distinct from each other; and as one year is requisite for the formation of a single layer of wood, these depositions are named annual layers or rings. In fig. 759 we have a representation of a stem three years old, and one of five years of age.
The number of rings in the stem do not invariably agree with the number of years the tree has been growing, but it may be accepted as a rule.
The stem is the medium of communication between the roots and leaves at first; but after a year this important duty is deputed to the cambium layers of new woody tissue, etc., and as time goes on the living power has accumulated immediately under the bark. So although the tree be quite hollow it will live. The interior has been closed up by deposition of wood and has decayed; but the life functions being relegated to the bark, the old tree lives on. If we remove the rind all round a tree it will die.
THE LEAVES.
When in the spring the young leaves appear upon the trees, and as summer advances they become fully developed, we are all grateful for the beautifully varied tints of green, and for the shade we can so fully enjoy. The study of leaves is a most interesting and instructive one, and nobody should omit to examine them. Their forms are infinite, or, at any rate, countless; their size as varied as their forms. Many attributes of the leaf will occur to every reader, and we will briefly describe these essential organs of plants. Air and light are necessary to the development of leaves, and their principal use is to present a surface to the food material which the plant absorbs. They breathe, as it were, and absorb the carbonic acid from the atmosphere. These functions are called “assimilation,” “transpiration,” and “respiration,” which we will detail by-and-by.
Leaves are distinguished according to position and duration. Some leaves have very simple forms, others are compound, so to speak. Some are plain and rounded, others are toothed, like the holly. The skeleton of a leaf is a very interesting study, and it will show the beautiful structure of these common objects. The delicate lines of the green leaf are “veins,” or sap-vessels, which convey the necessary nourishment. The leaves are called the “embryonic” (seed-like), the radicle, or root-leaf, the stalk-leaf, and the stipules, which grow at the base of stem-leaves, and the floral leaves, which bear the flowers or fruit buds. Leaves which are developed at the end of a chief axis are termed blossoms. Of course it must be understood that all the different kinds of leaves do not occur upon the same plant. The leaf may be accepted to mean the stem-leaf.
Leaves are folded up in various ways, and the manner in which this is accomplished is termed the vernation of the plant. The leaves of endogens and exogens differ in their veining. The former veins do not touch; there is none of that beautiful interlacing which we find in the exogenous leaves. In the former the veins rise from base to apex, curving as they advance, as in the well-known lily of the valley. This “nervous system” of the leaf is its “venation,” and the veins distributed in the blade or lamina of the leaf are twofold,—as remarked,—ascending in curves, or diverging from a central nerve called the “mid-rib.” These lateral nerves are either parallel or “reticulate”—that is, net-like.
We will now examine the forms of leaves which are regulated by the divergence and extension of the divisions of the mid-rib. Thus we get an orbicular, or peltate leaf; palmate, digitate, and pedate forms also occur, as may be seen in the illustrations, pages 672 and 673, where all the varied shapes can be studied. The leaf consists of a petiole or stalk, and the lamina or blade. The petiole is composed of bundles of vascular tissue; the lamina is formed by their extension, the interstices being filled with cellular tissue. So we perceive that the leaves and stems are composed of similar materials. To defend the tissue a skin, or epidermis, is placed upon the surface of the leaf, and this epidermis is full of breathing holes, or pores, called stomates (compare page 664). There are also cells filled with chlorophyl, which gives the leaf its green tint.
The petiole may be absent in a leaf, and when it is the leaves are termed sessile, or sitting leaves. These leaves sometimes coil round the stem, and are called “amplexicaul,” or stalk embracers. These are simple leaves. Compound leaves are composed of several blades or laminæ on a stalk, and are seldom sessile. SIMPLE LEAVES are almost innumerable in form and variety. Leaves may be equal or unequal, acicular or linear, rounded or oval, cordate or obcordate, reniform or sagittate, perfoliate or connate, crisp, whorled or truncate, retuse, acuminate or mucronate. The margins of simple leaves again are entire, deft, notched, crenated, crenulated, sinuous, or dentated. They are pinnatifid, multifid, or lobed, according to the divisions of the leaf.
Compound leaves are also divided into classes. The pinnate, as the rose-leaf, the clover trefoil. There are “doubly pinnate,” the digitate, as in the horse chestnut. Compound and simple leaves can be readily distinguished by inspection, for the former are “articulated” to the stalk and can be separated, but the simple leaves will be torn, for they are confluent throughout.
Leaves are evergreen or deciduous, accordingly as they retain or shed themselves. The ordinary leaf is deciduous; the fir and the yew and the imported laurel are evergreens. We have very few of these as natives of England, the ivy, yew, and fir being the three most common. Sometimes a plant peculiar to Killarney, and known as the arbutus, is included in the list. But the Scotch fir and the yew are distinctly native evergreens.
The detailed characteristics of leaves must be passed over until we come to the fly-catching leaves—such as Venus’ fly-trap, the droseras, and nepenthes, which appear to catch and devour insects for food. The Venus’ fly-trap may be examined, and we shall find the leaves covered with tiny and very sensitive hairs. Often a fly happens to alight upon the leaf, which is extended in a most innocent manner (see illustration). As soon as the fly settles the leaves close, and the digits lock tightly together, thus preventing the escape of the prey. The droseras, sarracenias, and nepenthes also kill their food. The sarracenias form curious cups, into which insects are enticed in search of fluid, and then, as in the case of the house-haunting cockroach, they cannot get out again. The nepenthes have a cup and lid for insect-catching, and within the cup a liquid is secreted.
We will close this portion of our subject with a quotation from a recent article upon botany referring to leaf arrangement. The writer says:—
“Efforts have been made to determine the laws to which these various modes of leaf-arrangement may be referable. The result is found in the doctrine of ‘Phyllotaxy,’ as it is called, the fundamental principle of the whole being that Nature, in the disposition of the leaves upon the stem, works upon precisely the same idea as that which is set forth so distinctly and elegantly in the common pine-cone; and, on a minor scale, in the beautiful cone of the female hop; not to mention the quasi-cones of many species of tropical palm, such as the Sagus and the Mauritia; nor to mention either, the very delicate repetition of the whole series in the florets of the Rudbeckia and the ripening fruits of Chaucer’s daisy. In every one of the flower and fruit arrangements mentioned, the idea is the spiral,—the same sweet old fashion which we have had in the twining stems of the convolvulus, the woodbine, and the scarlet bean; which comes out again in many a sea-shell, and in human ringlets; and this idea, according to ‘Phyllotaxy,’ governs the position of the leaves. Following alternate leaves up the stem, their sequence is clearly spiral. Through the non-development of internodes, they are brought closer and closer together; and even when the entire mass of foliage is concentrated and condensed into the rosulate form, as in the houseleek and the Echeverias, the spiral prototype is still distinguishable. The whole matter has been reduced to one of arithmetical exactitude; and for those who love calculations and “fractions,” the determination of the spirals, their continuity and intermixture, supplies abundance of curious entertainment. All three modes of leaf-arrangement are found in certain herbaceous plants, none disclosing this particular kind of playfulness more plainly than the common pyramidal Loosestrife, Lysimachia vulgaris, and the purple Lythrum of the waterside, in each of which very handsome wild flowers, alternate, opposite, and whorled leaves may be found in near neighbourhood. Alternate and opposite leaves are also met with, side by side, in various species of Myrtaceæ; and imperfectly, upon young shoots of the common ash-tree. The rule is, nevertheless, that there shall be uniformity, and in many of the largest natural orders the rule is never broken. In the Rosaceæ the stem leaves are invariably alternate; in the Gentianaceæ they are invariably opposite.”
FOOTNOTES:
[35] Dr. Carpenter.
LII. FLOWERING PLANTS
ORGANS OF INCREASE AND REPRODUCTION—THE FLOWER—THE CALYX—THE COROLLA—THE STAMEN—THE PISTIL.
Some of the simplest plants are propagated by spores, which are detached, and fall upon the ground to vegetate; but in the case of the higher orders the reproduction of species is a much more elaborate process, and is carried on by means of certain organs called flowers. Small buds, or ovules, are formed, which develop into seed. Plants also produce buds, which grow upon various parts of it, and are capable of reproducing their species. We will first speak of FLOWERS.
Flowers are not only the lovely blossoms we cut and place in our rooms, but the reproductive organs of plants which may be very plain and simple or gorgeous and fragrant, and in all probability the so-called flowers are few in comparison to the unrecognized flowers. Trees and bushes flower equally with the rose and the pink and carnation. Vegetables flower as well as the lily, though we do not recognize it so well. Let us now examine the “flower.”
Flowers may consist of four parts, but it is not absolutely necessary that they should contain more than two. The four portions of a complete flower are—
1. THE CALYX. 2. THE COROLLA. 3. THE STAMEN. 4. THE PISTIL.
The two last mentioned are essential. The four organs are placed around a pedicel or peduncle (flower stalk), and are known as floral whorls.
The CALYX is the outermost whorl of all when all exist. The portions of the calyx are known as sepals.
The COROLLA is usually the showy portion—the attraction of the flower. The pieces of the corolla are called petals. The sweet fluids of the plant are here concealed.
These parts—the calyx and corolla—are known as the floral envelopes, or “perianth.” The tulip has one whorl only, and it is called the envelope.
The calyx sometimes falls before the flower is full blown, as in the poppy. Its lower portion is the “throat,” and the shape of the organ varies, as will be seen by the illustrations.
The sepals are usually three to five in number. The poppy has two, and the well-known wall-flower four free—that is, disunited—sepals. The primrose possesses five. The calyx is the outside rim of all, and we may thus remember it, because its sepals alternate with the petals of the corolla. The petals may be formed cup-fashion, as in the lily of the valley, and here we have these sepals and petals in groups of three each.
The petals differ from ordinary leaves, and in them we find all the beautiful tints and the odour we imbibe from blossoms. The forms of corolla correspond to those of the calyx, and are called by the same names. But when corollas are absent the petals of course cannot provide the necessary colours for the flower. Then the calyx is gifted, and the sepals are brilliant. Thus Nature provides for everything.
Corollas are found with five or ten petals, and sometimes with three, six, and nine—the numbers always doubling or adding the original number. There may be four petals or eight, as in the “tetramerous” corolla (fig. 771). Instances of others are illustrated, and a plant whose petals, sepals, and stamens are numerically equal, or are multiples of each other, are termed “symmetrical.” The “regular” flower does not vary much, as the petals are of the same size and shape, but there are many “irregular” flowers—as the pea—in which portions of the calyx or corolla are of different shapes. The “labiate” and the “campanulate” are illustrated in figs. 774, 775, including the convolvulus and the snap-dragon. These are but a few examples of an almost endless diversity. The “regular” flowers—exemplified in the buttercup and convolvulus—always present the same figure to the observer.
To the petals the beautifully-varied colours of plants are due, and though it is not possible to enter upon the subject here, we may conclude that the various beauties of the colours of flowers are owing to light and air acting upon the various “colouring matters” contained in the plant. Seeds planted in a dark cellar will spring up pale; admit light, and they will become green, for light thus acts upon the chlorophyl. But the flowers of the plant are not so dependent upon light, as can easily be proved. Many interesting experiments have been made upon flowers by acids and gases.[36]
The STAMENS are the next in order for our consideration. They are found within the petals (or the calyx if no petals be present). Stamens vary very much in different plants both in number and general features—but, as in the case of petals, they keep, as a rule, to certain numbers and doubles of them. The stamen consists of two portions—a lower, thread-like part called the filament, and an oblong bag or head, termed the anther. This contains a powdery matter called pollen, and is the essential part of the stamen. The filament, which corresponds to the petiole of the leaf, may be absent, in which case the anther is called sessile. A lily will show the stamens perfectly, the anther being prominent in many other plants also, such as daffodils and fuchsias.
The stamens are very important organs with regard to the classification of plants—for number, length, and position, whether free or united, are all characteristic features. The length of filaments is always the same in the same kind of plant, and therefore is a very palpable test.
The anther contains the pollen, a powdery matter, usually yellow-coloured, but sometimes also red, brown, violet, or green-coloured. Pollen-grains vary from 1/20 to 1/300 of a line in diameter. Under a powerful microscope they appear as ellipsoidal, or sometimes spherical, triangular, polyhedral vesicles, filled with a granular semi-fluid matter. To effect fecundation, the pollen-grains must come into contact with a certain part of the plant which is intended to receive them, and which is called the ovule, and is found in the fourth or innermost verticil of the flower, the pistil. Of the further development of the ovule, we shall have occasion to speak in the paragraph treating of the seed.
At the proper time the anther opens and discharges its contents, the pollen-grains, some of which reach the place of their destination. The position of the stamens to the pistil is usually such that the latter can readily receive the pollen-grains. In many plants, however, the stamens are too short to reach the pistils; or the two essential organs of reproduction are in separate flowers, or even on different plants. In such cases, the conveyance of the pollen from the anthers to the pistils is effected by the agency of the wind, or by that of insects, and more particularly by the bee. If the anthers are removed from the flower previously to their opening, no fruit is produced.
Varieties of flowers and fruits are produced artificially, by shaking the pollen of one plant upon the flowers of another, deprived of the stamens. Many esteemed sorts of stock-gilliflowers and pinks have been produced in this way.
The pistil constitutes the fourth and innermost whorl, and occupies accordingly the centre of the flower and the apex of the axis, whose growth is terminated with the production of the fruit.
The pistil also is formed by one or several modified leaves, called carpels, in this part of the flower, and which exhibit a more marked resemblance in colour and structure to the ordinary leaves than the stamens and petals do. The formation of the pistil from the leaf may be considered to proceed in this manner: that the edges of the leaf are folded inwards and unite, whilst the mid-rib is prolonged upwards (fig. 776A). The place where the margins of the folded leaves are united is called suture or seam (ventral suture, in contradistinction to the mid-rib, which is called the dorsal suture); and it is here that the seed-buds or ovules are developed.
The pistil consists of two parts—viz., the ovary or germen, which contains the ovules or young seeds, a, and the stigma, b, either placed upon the ovary, or upon the style, or stalk, which is between the stigma and the ovary.
A pistil may be of one carpel (simple), or of more than one (compound). The carpels or the carpellary leaves are the “ovaries.”
The pistil is a very important test for the classification of plants; some trees have no pistils, and the ovules are consequently naked. Such plants are called gymnospermæ. The coniferæ (firs and pines) are thus recognizable, and the position of the ovule is very much that of the ordinary bud.
FOOTNOTES:
[35] Respecting artificial colouring of flowers, see page 329.
LIII. FLOWERING PLANTS (continued)
THE FLORAL AXIS—INFLORESCENCE—FRUIT—SEED—NUTRITION OF PLANTS—ABSORPTION OF CONSTITUENTS.
There are certain arrangements and mutual relations of the various portions of the flowers which we have mentioned that it is useful to consider. The floral axis refers to the position of the verticils, and inflorescence signifies the arrangement of the flowers on the stem. Flowers which possess both stamens and pistil are hermaphrodite; those with only stamens are male; those with the pistil female flowers. If both organs be absent the flower is neutral.
Plants bearing flowers in clusters form several distinct groups, to which appropriate terms are applied indicative of their respective form of flora arrangement.
In the examination of this kind of inflorescence (indefinite or axillary inflorescence), the first object of remark is the general or primary peduncle, termed rachis, and which bears numerous leaflets called bracteoles or bractlets, from whose axils arise the pedicellate or sessile flowers. The lower bracts often produce no flower-buds in their axils, and form instead a whorl surrounding the heads of flowers on the primary axis, and which is called involucre (as in the sun-flower, for instance).
The different varieties of axillary inflorescence are determined principally by the elongation or depression of the axis, the presence or absence of stalks to the flowers, and the form and nature of the bracts. We distinguish—
1. (1) The spike (fig. 777). In this form of inflorescence, sessile or short-stalked flowers are arranged along the rachis in the axils of the bracts; the spike is said to be compound when small spikes or spikelets arise again from the bracts of the secondary axis. (2) The catkin or amentum (fig. 777 [2]); a spike, usually pendulous, which falls off, rachis and all, by an articulation, as in the willow or hazel. 3. The spadix, a thick fleshy spike (fig. 777 [3]); examples, arum and calamus. 4. The cone, a fruit-bearing spike, covered with scales (fig. 777 [4]); examples, the coniferæ. 5. The raceme or cluster, a spike with the flowers on longer pedicels (fig. 778); examples, the currant. 6. The panicle, a branching raceme (fig. 779, Yucca gloriosa). 7. The thyrsus, a dense panicle, with longer peduncles in the middle than at the extremities; example, lilac. 8. The corymb, a raceme, in which the lower flower stalks are elongated and raised to nearly a level with the upper (fig. 780)—example, cerasus mahaleb. 9. The compound or branching corymb, a corymb in which the secondary axis again sub-divides; example, Pyrus terminalis. 10. The umbel: in this form the primary axis is greatly depressed, and the peduncles arise from a common point, and spread out like radii of nearly equal length, a whorl of bracts (involucre) surrounding the common base. In the compound umbel (fig. 781), Daucus carota, the secondary axis ends in small umbels surrounded by bracts, which is termed an involucel. This is observable in the umbelliferous plants—carrot, parsley, hemlock, etc.
A very peculiar kind of inflorescence, which characterises the great family of the compositæ, is illustrated by fig. 783. We see here the enlarged floral axis or receptacle, a, surrounded by several whorls or bracts, b b, which constitute a general involucre; the membranous bracts, (paleæ), b´ b´, seen in the receptacle, bear in their axils the sessile florets, c and d, which either have a calyx, e e, or not. The florets on the receptacle are either all of them tubular (d) or ligulate (tongue or strap-shaped); florets (c) are associated with the tubular ones. The receptacle is not always flat, but frequently presents a convex, globular, conical, concave, etc., shape.
In the absence of paleæ the receptacle is said to be naked. The florets at the margin, or circumference, are termed marginal flowers, or flowers of the ray; the florets in the disc (centre), central flowers, or flowers of the disc.
Some plants bear male and female flowers on the same stem. These are termed monæcious plants. The oak is an instance. The diæcious plants are those which bear stamens and pistil, or separately, on different plants, like willows. We will now glance at the functions of the stamens and pistil. The ovule has been mentioned as a tiny body in the ovary, and it consists of a nucleus, and cellular tissue surround it, leaving a small hole called the micropyle, into which the pollen tube enters after passing through the ovary. As in the animal creation, the unions of different families succeed best; no close relationship will fertilize so well as with other flowers.
Fertilization is accomplished in two ways; (1) by the action of the wind, by which the pollen is carried away to other plants; and (2) by means of insects—the bee particularly. These flowers have distinctive qualities relatively. In the case of the pine the pollen is powdery; so those plants which are thus fertilized are the diæcious species, which include the poplar, the oak, and the birch, as well as the pines. These are all wind-carried pollen plants. The nettle is illustrated here with male and female flowers.
Plants fertilized by insects are visited by them, and they carry away upon their heads, or bodies, the pollen, which is then thrust into the stigma by the insect; or perhaps birds may carry the pollen in the same way after sipping the nectar, and thus playing an unconscious, but most important, part in the economy of nature.
We always find the ovule at the termination of an axis; it is unable to form a seed alone. The pollen grains must fertilize it, and in consequence many ovules come to nought. The ovule is produced in the pistil, which, as before stated consists essentially of two parts—the ovary and the stigma; the latter secretes a fluid to hold the pollen. We annex the representation of a highly-magnified pistil (vertical section, fig. 786_a_). The pollen grains are indicated by d, attached to stigma, c, projecting through the style, b, into the ovary, a, and passing through the ovules.
With the transmission of the pollen to the ovary of the pistil, the functions of the anther and stigma terminate; accordingly these parts of the flower rapidly wither and decay after fertilization. The filaments, the style, and the petals speedily participate in the decay, but the sepals remain sometimes persistent in an altered form. The ovary and its contents alone proceed in their further development, and undergo material changes, in which, however, the bracts and the calyx often participate.
The fully developed and matured ovule, the seed, is, of course, regarded as the essential part of the fruit; the enlarged ovary forms the pericarp, enclosing the seed. The form of the pericarp determines the external appearance of the denomination of the fruit. The structure of the fruit, and the arrangement of its parts depends in a great measure upon the number and position of the carpellary leaves in the pistil, and the manner and extent of their union, and the extent to which their edges are folded inwards.
The carpellary leaves occupy the summit of the floral axis. The axis terminates either in one single carpel, in which case the ovary is one-celled, or unilocular; or the axis is surrounded by several carpels, in which case the manner of their union determines the number of cells in the ovary.
THE FRUIT.
The carpels are the chief agents in the formation of the fruit, and they form the endocarp (core), and sometimes the whole pericarp, or seed-vessel. Upon the nature of the various parts and the changes they undergo during the ripening of the seeds the nature of the fruit depends. The fruits are classified, some being the produce of a single carpel, others of several united carpels.
Fruit, in botany, is by no means limited to the juicy products of trees or plants which are so refreshing in the summer weather, and so acceptable in any form. In plant life the herb yielding seed produces a fruit equally with the orange or the apple. The fruit is the outcome of the varied processes of the plant. We may trace the plant from its tiny, sometimes very minute seed, through stem to flower and seed again. “In the final struggle, even when life is hopeless, and starvation, in consequence of drought, is imminent—when all is hopeless and barren, the plant will make an effort to produce its fruit and flower.” This is a very touching and interesting fact in nature—this last attempt to beautify the earth and to propagate its species for the use of man.
Fruit, then, is not limited to the market and the stall.
This statement scarcely needs proof; but if we consider for a moment the number of “wild” fruits—the parents, probably, of our table-fruits—we find many we cannot eat. In short, out of the hundred thousand plants which bear flowers scarce one two-hundredth part serve us as producers of edible fruits.
The fruit is the result of the flower, and if any objection be made by readers on the part of the common fig, it will be found that this appreciated fruit really consists of male and female flowers that are fertilized by the action of minute insects, which enter and depart (sometimes they die, and are found dead and black in the figs). No blossom is perceived on the tree, because within the green sac the so-called “seeds” (really the fruits) are developing. A fig is a sac full of fruits.
The legume or pod is formed of a single carpel bearing seeds. We annex illustrations of the pod. The covering is called the pericarp, and the parts when opened separate into valves. Dehiscent fruits shed their seeds, indehiscent fruits do not; they lie within the seed-vessel, like the acorns and nuts. These are dry fruits, but there are others of a soft nature, such as apples or gooseberries.
Fruits are variously named, and underneath will be found a list. We have the aggregate, like the mulberry, etc.; the dehiscent fruit of one carpel like the pea, etc.; the simple fruits as cherry, nettle, wheat, etc. The dandelion fruit is often a precious object in children’s estimation, as it is blown away to ascertain the time. There are indehiscent fruits with many carpels,—the common buttercup, for instance, and the strawberry. A list is added.
a. FRUITS WHICH ARE THE PRODUCE OF A SOLITARY CARPEL.
1. The gymnospermous fruit, where the seed lies naked in the axils of the ligneous bracts, as in the cone of the fir and spruce tribe.
2. The legume or pod, which is formed of a solitary carpel bearing seeds on the ventral suture. It characterises the pea and bean tribe (leguminosæ).
3. The follicle is a mature carpel containing several seeds, and opening by the ventral suture. There are usually several follicles aggregated together; examples, larkspur, monkshood, evergreen.
b. FRUITS WHICH ARE THE PRODUCE OF SEVERAL CARPELS UNITED.
4. The capsule consists of two or more carpels, either simply laterally united (one-celled or unilocular capsule), or folded inwards towards the axis, but without reaching it (spuriously multilocular capsule), or uniting with the axis (bilocular, trilocular, multilocular capsule). Examples of capsular fruit—mignonette, balsam, violet, poppy, etc.
5. The siliqua or long pod is formed of two carpels, and longitudinally divided into two parts by a spurious dissepiment called the replum; examples—cabbages, stock, wallflower, etc. The silicula is a broad and short pod; examples—Iberis, shepherd’s-purse, etc.
6. The cariopse (caryopsis, having the appearance of a nut), is a monospermous or one-seeded fruit, with an indehiscent membranous pericarp, closely investing the seed or incorporated with it; examples—rye, wheat, and other grains.
7. The achænium is a dry, monospermous, indehiscent fruit with one seed; examples—cashew, ranunculus, strawberry, etc.
8. The nut or glans is a one-celled, indehiscent fruit, with a hardened coriaceous or ligneous pericarp; examples—hazel-nut, acorn, etc. The nucula, or little nut, is a cariopse, with a solid coriaceous pericarp; examples—buckwheat hemp, etc.
9. The berry (bacca) is a pulpy, succulent fruit, with soft rind; examples—the gooseberry and the currant. The pepo or peponida (pumpkin), illustrated by the fruit of the gourd and melon, and the hesperidium, illustrated by the fruit of the orange and lemon, are modifications of the berry.
10. The drupe (drupæ, unripe olives); the mesocarp is generally pulpy and succulent, the endocarp hard; examples—the cherry, the peach, the plum, etc.
11. The pome (pomum, or apple); the outer parts of the pericarp form a thick cellular, eatable mass; the endocarp (core) is scaly or horny, and encloses the seeds within separate cells; examples—the apple, pear, etc.
Fruits consisting of the floral envelopes and the ovaries of several flowers united into one, are termed multiple or anthocarpous; the sorosis (cluster-fruit: example—the pine-apple, the breadfruit, the mulberry), the sycosis (fig-fruit), and the strobilus (fir-cone), form varieties of the anthocarpous or multiple fruit.
NON-FLOWERING PLANTS.
The cryptogamia or acrogens is the botanical term for these plants, of which we must be very brief in our description,—not that the subject is not worthy of a much larger space than we can devote to it, but our pages are not elastic.
There are numbers of plants without pistils or stamens properly so called. They are hidden from human observation—buried out of sight; and in the fern, moss, and other primitive plants they are thus hidden. There are several families of the cryptogamia, but two main sections include them all—viz., the cormogens and thallogens. These are sometimes known as cormophytes and thallophytes, but the former will be our terms, and they include the ferns, algæ, lichens, and mosses, with many other families, which we do not propose to examine in this summary sketch. The microscope will here be a great aid if not always absolutely necessary for any close investigation.
We are all familiar with the appearance of ferns, and we may commence with a few observations concerning them. They are an extensive family and very beautiful, some of the tropical species being particularly noticeable for elegance. We are here mostly concerned with the development of the plant. The polypod ferns fructify under the leaves or “fronds,” which open from a ball. The seed-cases or sorri are situated at the back of the fronds in brown spots, and when examined they will be found to be collections of capsules like tiny cases. There is a kind of band at the upper part which at the proper time is extended, and tearing open the capsule releases the seeds. These seeds or “spores” are very minute, and not properly seeds but buds, every one of which can generate seeds. So if we try to grasp in imagination the generating powers of a few fern fronds, we shall miserably fail in the attempt.
Some ferns have the “spores” upon the summit of the frond. The osmundas belong to this family, and are known to all as the “flowering fern,” a contradiction palpable enough under the circumstances. The beautiful dust upon some ferns has been mistaken for “spores” by many people, but it is merely a natural ornament of the plant. The venation and vernation of ferns are very curious, but in the determination of ferns the only sure way is to consider the sorri and the venation. The differences that puzzle may be little or great, but when the sorri have been examined all doubts will be set aside.
There are about three thousand varieties of ferns known, and we give a few illustrations of them, although any detailed description is out of the question, for we have to mention the beautiful mosses of which there are in Britain more than five hundred different species, all extremely beautiful, perfectly innocuous, and even beneficial.
THE MOSSES AND ALGÆ.
These plants are extremely lowly in the score of creation, and also in stature. Very few mosses attain any elevation, only the “sporangia” shoot up, and the plants are very delicately formed, the leaves being all of the same pattern. They are common in damp situations, and thrive in woods, streams, and banks. The Fontinalis is a river moss, while the Hypnum is found in hedges. The Lycopodiaceæ or the club-moss family is intermediate between ferns and mosses. They are found in warm, moist climates, and contain a sort of brimstone. They grow well with ferns under glass.
The Musci or moss-family proper are useful in various ways. We have also the liverworts, which bear some resemblance to lichens. They grow between stones near water, or in damp situations. There are two distinct families, both beautiful when examined, and are named Marchantiaceæ, and Jungeramanniaceæ, or scale moss.
The Thallogens or Thallogenæ include algæ, lichens, and fungi, which are the lowest of the plants, and all very much alike. The algæ are termed “protophytes,” and consist of living cells propagating by subdivision, or union. The thallogens have therefore no distinct axes, leaves, or stomata.
The algæ are thus simply cellular plants found in salt or fresh water, hot and cold. They sometimes appear as “slime.” Some contain silicia, and are termed Diatomaceæ, and these propagate by subdivision, and when they die their shelly covering remains, and we find the shells or cases in all earthy formations. These diatomaceæ have been raised from the beds of oceans, and Atlantic soundings have revealed their presence,—as mud, when examined, proves to be these remains of vegetable shells. Thus the infinitely little in the animal and vegetable worlds meet at the bottom of the sea, as well as on dry land.
There are marine and fresh-water algæ—the former familiar to us as seaweeds which possess air-bladders that children love to explode, and which assist the algæ to float. They attach themselves to rocks, generally at the base; the lovely colours of seaweeds are well known. They will be recognized under the name of “tangle” (fucus), which, when burned, gives kelp and barilla, which is full of iodide and sodium. The Sargasso Sea is composed of miles of algæ which live in the open ocean. The Carrageen or Irish moss is very nutritious and useful in consumptive cases. Indeed, all algæ, if not absolutely useful, are certainly not deleterious. The “bladder-wrack” was formerly useful for the production of soda.
“The life-history of one of these uni-cellular plants in its most simple form, can scarcely be better exemplified than in the Palmogeœa macrococca, one of those humble forms of vegetation which spreads itself as a green slime over damp stones, walls, etc. When this slime is examined with a microscope, it is found to consist of a multitude of green cells, each surrounded by a gelatinous envelope; the cell which does not seem to have any distinct membranous wall is filled with granular particles of a green colour, and a ‘nucleus’ may sometimes be distinguished through the midst of these. When treated with tincture of iodine, however, the green contents of the cell are turned to a brownish hue, and a dark-brown nucleus is distinctly shown. Other cells are seen, which are considerably elongated, some of them beginning to present a sort of hour-glass contraction across the middle; in these is commencing that curious multiplication by duplicative subdivision which is the mode in which increase nearly always takes place throughout the vegetable kingdom.”[37]
LICHENS are numerous, and may be found upon the bark of trees in dry forms of grey and yellow growth, and on walls and old stones in our graveyards. On the hills we find them growing upon the granite, and it would appear that they prefer stone to any other holding ground. The Arctic lichens form the principal food of the useful reindeer, and “Iceland moss” is represented as wholesome for man. Lichen is derived from the Greek term for “wart.”
The FUNGI are very important, and with them we will close our summary. They include the favourite mushrooms and poisonous toad-stools, with many other “fungous growths,” from the “mould” on the jam pot to the mushroom.
Some of these fungi are peculiar to the substances upon which they exist, and are in numerous instances destructive. The microscopic fungus Puccinea graminis is the parasite which fixes itself to corn, and produces the disease known as mildew, and the Uredo segetum (another microscopic fungus) causes the “smut”; the “bunt” is caused by the Uredo fœtida, and the “spur” or “ergot,” which attacks rye, is caused by the Acinula clavis. These fungi completely destroy the grain of corn in which they form, and propagate in the most rapid manner; the ergot is moreover a dangerous poison to those who eat the bread made of rye infected by it. The truffle is a kind of underground fungus, and is esteemed a dainty. Mushrooms are also fungi, and several species are sufficiently wholesome; these are the field mushroom and the fairy-ring mushroom.
Any organic substance will shortly become covered with this “mould” or mildew. The air is so full of the germs of animal and vegetable life that, as it penetrates everywhere, the smallest supply must contain some germs; and these, under a powerful microscope, present most beautiful forms and colours. We annex (fig. 822) some of these forms highly magnified. They are deposited by the air, and the substance into which they happen to fall determines the kind of life which is to inhabit it. A few of these spores only come to maturity.
We again take the liberty to quote Dr. Carpenter on this subject. He says:—
“There are scarcely any microscopic objects more beautiful than some of those forms of mould or mildew which are so commonly found growing upon the surface of jams and preserves, especially when they are viewed with a low magnifying power and by reflected light; for they present themselves as a forest of stems and branches of extremely varied and elegant forms, loaded with fruit of singular delicacy of conformation, all glistening brightly on a dark ground.
“The universality of the appearance of these simple forms of fungi upon all spots favourable to their development, has given rise to the belief that they are spontaneously produced by decaying substances, but there is no occasion for this mode of accounting for it, since the extraordinary means adopted by nature for the production and diffusion of the germs of these plants adequately suffices to explain the facts of the case.
“The number of sporules which any one fungus may develop is almost incalculable; a single individual of the “puff-ball” tribe has been computed to send forth no fewer than ten millions. And their minuteness is such that they are scattered through the air in the finest possible dust, so that it is difficult to conceive of a place from which they should be excluded.”
Pure water exposed to the air does not afford nourishment to the germs which fall into it, till a sufficient number of them shall have been deposited to form a food for those which come after them; but if we mix with the water any soluble vegetable or animal matter, in a short time the microscope will detect the growth of the germs that are being deposited, for where nourishment is, there only can they be developed. These germs are capable of existing for an indefinite period, either floating in the water, or blown about by the air, and have been detected hundreds of miles from land; the rigging and sails of ships far away from shore are often covered with what sailors suppose to be sand blown from the land, but which are organic substances, either vegetable or animal. According to Humboldt, the Red Sea has derived its name from the fact that at certain seasons the surface of the water has a reddish appearance, and this (as he says) he was fortunate enough to observe, which colour he found to be due to myriads of red fungi, which had formed on the surface. The seeds of some plants are furnished with minute wings or plumes, which cause them to be borne on the air or floated on the water (fig. 824), to fertilise some barren spot, perhaps a coral reef, which has at length reached the surface of the water, and which ascends no higher, for the little creatures which built it are aquatic, and cannot live exposed to the air; this coral reef now becomes a receptacle for seaweed and fungi, which float on the surface of the ocean are washed on to the reef, die, decay, and leave behind a thin layer of mould, which process being repeated again and again, forms an elevated edge to the reef, enclosing a lake, or “lagoon” as it is called, the waters of which evaporate, and the space is filled up in the same way as the edge was formed, together with the excrements of birds, etc., forming layer after layer of mould, and the surface becomes fit for the growth of larger seeds, as the cocoa-nut, banana, etc., which are drifted on to it by the waves; in this way a coral reef becomes an island fit to be inhabited by man and other animals.
It is impossible for any person not accustomed to observe the manner of the propagation of the fungi, to understand a written description, for the fructification of these plants are very varied in the manner of the development of the spores. They are not generally hurtful, but much caution should be observed in the matter of the mushroom, which may be distinguished by the pale pink and black of the under part. There are many poisonous fungi, but the greater number are harmless, though they are not intended for food. They simply clear away the decaying growths, and act as safety-valves to Nature by carrying away what is not required, to give it to the air again to be renewed into life.
The vegetable kingdom forms the link between the minerals and the animals. The vegetable derives food and nourishment from water, carbonic acid, and ammonia, which are, as we already know, made up of certain elements, and thus supply us all with food. They give out oxygen for the use of animals, and are thus, in another sense, the source of life. The growth of a plant is very interesting, and we may conclude by following it.
The seed is sown, and the cells of the “cellular tissue” become developed, passing some upwards, some downwards, to form a radicle or plumule, as explained. The latter carries up the cotyledon, which begins to decompose carbonic acid from the atmosphere, and fixing the carbon as woody fibre. The leaves are then formed and more fibres, and so on for every leaf; thus the number of woody fibres which form the trunk of a tree is in proportion to the number of leaves which that tree has borne, from which we come to the conclusion that the size of the trunk of a tree is the sum of all its branches. While all this is going on, the cellular tissue of the downward part or radicle also becomes developed and divides out into roots, on the surface and at the extremities of which are minute cellular bodies called “spongioles” (from their power of absorbing moisture), which take up the fluid of the earth which surrounds them; this moisture ascends through the vessels of the plant till it arrives at the surface of the leaves, where it is exposed to the action of light and sunshine. The ascent of the moisture of the earth was first correctly explained by Du Trochet, and is owing to a peculiar power which he discovered, and which is called “Endosmose”; this consists in the tendency which a fluid has to penetrate a membrane on the other side of which is a fluid of greater density than itself. This may be seen by the following experiment: obtain a piece of glass tubing about a foot long, having the end blown out into the form of a bell, as in fig. 825, tie a piece of bladder over the expanded end and fill it partly with syrup or gum-water, so that this shall rise in the stalk about an inch; place this in a glass of water with the bladder downwards, and the fluid will be seen slowly to rise in the stalk, so that in perhaps an hour it will rise to the top. This apparatus resembles one of the spongioles at the extremity of the fibre of a root.
The rain falling through the air carries with it a certain amount of carbonic acid and ammonia, which the air always contains, and it is the whole source of the nitrogen which forms a very important part of the bodies of plants and animals. When the rain arrives at the surface of the earth, it sinks down into it and carries with it all soluble vegetable or animal matter which it meets with, together with any soluble earthy matter which may exist in the soil; this forms the sap of the tree. When it arrives at the surface of the leaf, the watery part of it combines with the carbonic acid of the air (through the influence of light), and appropriating its carbon, gives out the oxygen; this is the true respiration of plants, and is exactly the reverse of what takes place during the respiration of animals, in which case oxygen is absorbed and carbonic acid given off. The carbon thus retained by the plant combines with the elements of the water to form the solid green substance called chlorophyl, which is the basis of all the tissues of the plant; the ammonia is also decomposed, and its nitrogen combining with the oxygen and hydrogen of the water, and the carbon of the carbonic acid forms those compounds which constitute the most nourishing parts of vegetables, such as albumen, gluten, etc., and of which all the animal tissues are built up, for the production of these organic substances takes place in the vegetable only, animals simply appropriating them for their food. The sap which reaches the leaf is not all converted into chlorophyl, but also into those peculiar juices which are found in plants, some of which contain sugar, some gum, others (as the pine tribe) turpentine, and in the laurel tribe camphor, all of which are substances containing much carbon; moreover the solid wood and bark are deposited from these juices as they descend from the leaf after having been acted on by light (or the actinic power associated with it). Now, as the water, ammonia, and carbonic acid which descend with the rain are from the air, and as the vegetable is formed wholly by their absorption, it may be fairly said that the vegetable kingdom (and therefore the animal) feeds upon the air, and that the trees do not grow out of the earth, but into it.
CLASSIFICATION OF PLANTS.
For the groundwork of the system of classification which universally obtains at present, we are indebted to Linnæus, a Swede, born in 1707. In his classification of plants, Linnæus followed two different methods. In the one, he based his division of plants in classes and orders, upon certain peculiarities in the floral organs. This system, being thus founded on characters taken from certain parts of the plant only, without reference to others, and having something artificial in it, has for that reason been termed the artificial system, but it is now more generally known as the Linnæan system. In the other method, he arranged the plants according to certain general resemblances and affinities, in natural orders or families. This system, which is known as the natural system, has subsequently been much improved.
We use the term species, to designate a number of individual plants, which, in all essential and unvarying characters, resemble each other more closely than they do any other plant; the term genus or kind, to designate an assemblage of nearly allied species, agreeing with one another in general structure and appearance more closely than they do with any other species. Here, too, it must be obvious, that while all parts of the plant may furnish specific characters, the character of the genera are taken exclusively from the parts of fructification.
In the name of a plant both the genus and the species are given. The name designating the genus is called the generic name of the plant, the one designating the species, the specific or trivial name. Thus, for instance, we have the genus Viola, which includes the species Viola odorata, sweet violet; Viola canina, dog violet; Viola tricolor, heart’s-ease.
It is necessary to give the Latin names of plants, as the common name differs, not only in different countries, but even in different parts of the same country.
An assemblage or group of allied genera, agreeing in their general characters, though differing in their special conformation, is called an order or family of plants.
The sunflower, the daisy, the aster, and the dahlia, are, for example, plants of different genera, but which, all of them, belong to the same order or family.
All plants are divided into three primary classes—viz., Dicotyledons, Monocotyledons, and Acotyledons, as has been stated already.
A proper degree of familiarity with the systematic classification of plants is of the very highest importance to the student. A successful pursuit of this branch of the botanical science presupposes a thorough knowledge of the structure and physiology of plants, and requires, moreover, the aid of attentive observation, and also some diligence in collecting and arranging plants.
THE ARTIFICIAL OR LINNÆAN SYSTEM OF CLASSIFICATION.
In this system plants are divided into twenty-four classes; twenty-three of these contain the Dicotyledons and Monocotyledons indiscriminately; the twenty-fourth class contains the Acotyledons.
The first twenty-three classes are founded on the number, position, relative lengths, and connection of the stamens. The twenty-fourth comprises the plants with inconspicuous flowers. Every class is subdivided again into several orders. This division depends, in the first thirteen classes, on the number of the styles; in classes XIV. and XV. on the nature of the fruit; in classes XVI. to XVIII. and XX. to XXII. on the number of stamens; in classes XIX. and XXIII. on the perfection of the flower. In class XXIV. the orders are formed according to natural affinities.
TABULAR VIEW OF THE LINNÆAN SYSTEM OF CLASSIFICATION.
A.—FLOWERS PRESENT (Phanerogamia).
I. Stamens and pistil in every flower (hermaphrodite).
1. Stamens free.
a. Stamens of equal length, or not differing in definite proportions.
Number of Stamens. 1 Class 1. Monandria. 2 ” 2. Diandria. 3 ” 3. Triandria. 4 ” 4. Tetrandria. 5 ” 5. Pentandria. 6 ” 6. Hexandria. 7 ” 7. Heptandria. 8 ” 8. Octandria. 9 ” 9. Enneandria. 10 ” 10. Decandria. 11-19 ” 11. Dodecandria. 20 or} inserted on calyx ” 12. Icosandria. more } ” receptacle ” 13. Polyandria.
b. Stamens of different lengths, two long and two short ” 14. Didynamia. four long and two short ” 15. Tetradynamia
2. Stamens united by filaments in one bundle ” 16. Monadelphia. ” ” in two bundles ” 17. Diadelphia. ” ” in more than two bundles ” 18. Polyadelphia. ” by anthers (compound flowers) ” 19. Syngenesia. ” with pistil on a column ” 20. Gynandria.
II. Stamens and pistil in different flowers (unisexual) on the same plant ” 21. Monœcia. on different plants ” 22. Diœcia.
III. Stamens and pistil in the same or in different flowers, on the same or on different plants ” 23. Polygamia.
B.—FLOWERS ABSENT ” 24. Cryptogamia
TABULAR VIEW OF CLASSES AND ORDERS.
---------------------+---------------------------------+-------------- Classes. | Orders. | Examples. ---------------------+---------------------------------+-------------- | | I.—MONANDRIA | Monogynia one style | Hippuris. One stamen. | Digynia two styles | Callitriche. | | II.—DIANDRIA | Monogynia one style | Syringa. Two stamens. | Digynia two styles | Anthoxanthum. | Trigynia three do. | | | III.—TRIANDRIA | Monogynia one style | Iris. Three stamens. | Digynia two styles | Hordeum. | Trigynia three do. | Holosteum. | | IV.—TETRANDRIA | Monogynia one style | Scabiosa. Four stamens. | Digynia two styles | Gentiana. | Trigynia three do. | | | V.—PENTANDRIA | Monogynia one style | Borago. Five stamens. | Digynia two styles | Fœniculum. | Trigynia three do. | Sambucus. | Tetragynia four do. | Parnassia. | Pentagynia five do. | Linum. | Polygynia six and more do. | Myosurus. | | VI.—HEXANDRIA | Monogynia one style | Lilium. Six stamens. | Digynia two styles | Oxyria. | Trigynia three do. | Rumex. | Tetragynia four do. | Alisma. | Polygynia many do. | | | VII.—HEPTANDRIA | Monogynia one style | Trientalis. Seven stamens. | Digynia two styles | | Trigynia three do. | | Heptagynia seven do. | | | VIII.—OCTANDRIA | Monogynia one style | Daphne. Eight stamens. | Digynia two styles | Chrysosplenium. | Trigynia three do. | Polygonum. | Tetragynia four do. | Paris. | | IX.—ENNEANDRIA | Monogynia one style | Nine stamens. | Trigynia three styles | | Hexagynia six do. | Butomus. | | X.—DECANDRIA | Monogynia one style | Pyrola. Ten stamens. | Digynia two styles | Dianthus. | Trigynia three do. | Silene. | Pentagynia five do. | Lychnis. | Decagynia ten do. | | | XI.—DODECANDRIA | Monogynia one style | Lythrum. Twelve to nineteen | Digynia two styles | Agrimonia. stamens. | Trigynia three do. | Reseda. | Pentagynia five do. | | Dodecagynia twelve do. | Sempervivum. | | XII.—ICOSANDRIA | Monogynia one style | Prunus. Twenty or more | Digynia two styles | Cratægus. stamens inserted | Trigynia three do. | Sorbus. on the calyx. | Pentagynia five do. | | Polygynia many do. | Rosa. | | XIII.—POLYANDRIA | Monogynia one style | Papaver. Many stamens | Digynia two styles | Pæonia. inserted on the | Trigynia three do. | Aconitum. receptacle. | Tetragynia four do. | | Pentagynia five do. | Nigella. | Hexagynia six do. | | Polygynia many do. | Ranunculus. | | XIV.—DIDYNAMIA | Gymnospermia four naked seeds | Lavandula. Two long and two | Angiospermia seeds in capsules | Linaria. short stamens. | | Labiate and | | Personate Flowers. | | | | XV.—TETRADYNAMIA | Siliculosa broad and short pod | Capsella. Four long and two | (silicula), and | short stamens. | style | Cruciferous | Siliquosa long pod (siliqua); | Brassica. Flowers. | stigma sessile | | | XVI.—MONADELPHIA | Pentandria five stamens | Erodium. Stamens united in | Enneandria nine do. | one bundle. | Decandria ten do. | Geranium. | Dodecandria 11-19 do. | Malva. | Polyandria many do. | | | XVII.—DIADELPHIA | Pentandria five stamens | Stamens united in | (two above and three below.) | two bundles (one | Hexandria six stamens | Fumaria. generally | (three right, three left, or | containing nine | three above and three below.) | enclosed in a | Octandria eight stamens | Polygala. tube, and one | (four above and four below, | free). | all united at the base.) | Papilionaceæ. | Decandria ten stamens | Pisum, Trifolium | (one above and nine below, | Genista. | united in a cleft tube | | surrounding the ovary.) | | | XVIII.—POLYADELPHIA | Pentandria five bundles | Stamens united in | (each bundle bearing five | more than two | anthers = 25 stamens.) | bundles. | Dodecandria twelve stamens | | (each bundle bearing three | | anthers = 36 stamens.) | | Icosandria many stamens in | Citrus. | bundles, inserted on the calyx | | (20 stamens in bundles bearing | | an unequal number of anthers.) | | Polyandria many stamens in | Hypericum. | three, five, and nine bundles, | | inserted on the receptacle. | | | XIX.—SYNGENESIA | Polygamia æqualia, florets all | Lactuca. Five stamens, | hermaphrodite. | filaments free, | Polygamia superflua, florets of | Aster. anthers united, | the disc hermaphrodite, those | flower | of the ray pistilliferous and | monopetalous, | fertile. | florets united on | Polygamia frustranea, florets | Helianthus. a disc. Compositæ. | of the disc hermaphrodite, | In the first four | those of the ray neutral. | orders only a | Polygamia necessaria, florets | Calendula. common calyx. | of the disc staminiferous, of | | the ray pistilliferous. | | Polygamia segregata, a common | Echinops. | calyx including all the | | florets, and a separate | | involucre for each. | | Monogamia, anthers united, | | flowers not compound. | | | XX.—GYNANDRIA | Diandria two anthers | Orchis. Stamens and | Triandria three do. | pistil united. | Tetrandria four do. | | Pentandria five do. | | Hexandria six do. | Aristolochia. | Decandria ten do. | | Dodecandria 11-19 do. | | Polyandria twenty or more do. | | | XXI.—MONŒCIA | Monandria one stamen | Arum. Stamens and pistils | Diandria two stamens | Lemna. in different | Triandria three do. | Carex. flowers on the | Tetrandria four do. | Urtica. same plant. | Pentandria five do. | Amaranthus. | Hexandria six do. | | Heptandria seven do. | | Polyandria more than seven do. | Quercus. | Monadelphia stamens united | Pinus. | Syngenesia stamens united by | | their anthers. | | Gynandria stamens and styles | | united | | | XXII.—DIŒCIA | Monandria one stamen | Salix. Stamens and pistils | Diandria two stamens | in different | Triandria three do. | Ficus. flowers on | Tetrandria four do. | Viscum. different plants. | Pentandria five do. | Cannabis. | Hexandria six do. | Loranthus. | Octandria eight do. | Populus. | Enneandria nine do. | Laurus. | Decandria ten do. | | Dodecandria 11-19 do. | Stratiotes. | Polyandria many do. | | Monadelphia stamens united in | Juniperus. | one bundle. | | Syngenesia stamens united by | | the anthers. | | Gynandria stamens and styles | | united. | | | XXIII.—POLYGAMIA | Monœcia, hermaphrodite, | Acer. Stamens and pistil | staminiferous, and | in the same, or in | pistilliferous flowers on the | different flowers, | same plant. | on the same or on | Diœcia on two plants | Fraxinus. different plants. | Triœcia on three plants | | | XXIV.—CRYPTOGAMIA | Filices Ferns | Aspidium. Organs of | Musci Mosses | Spagnum. fructification | Hepaticæ Liverworts | Marchantia. concealed (flowers | Lichenes Lichens | Cetraria. inconspicuous). | Algæ Seaweeds | Fucus. | Fungi Mushrooms | Agaricus. ---------------------+---------------------------------+--------------
With all its imperfections, the artificial system has this advantage, that the character on which it is founded is sufficiently conspicuous (that is, of course, with the plants in full flower) to render it generally easy to ascertain the class and order of a plant. At all events, it may serve as a useful artificial key, and as such may be combined advantageously with the natural system.
114. NATURAL SYSTEM (JUSSIEU’S).
Classes. I. Acotyledons 1st Class.
II. Monocotyledons Mono-hypogynæ (stamens hypogynous) 2nd ” Mono-perigynæ (stamens perigynous) 3rd ” Mono-epigynæ (stamens epigynous) 4th ”
III. Dicotyledons. Monoclines, flowers hermaphrodite. Epistamineæ (stamens epigynous) 5th ” Apetalæ (no petals) Peristamineæ (stamens perigynous) 6th ” Hypostamineæ (stamens hypogynous) 7th ” Monopetalæ (petals united) Hypocorollæ (corolla hypogynous) 8th ” Pericorollæ (corolla perigynous) 9th ” Epicorollæ (corolla epigynous) Synantheræ (anthers united) 10th ” Chorisantheræ (anthers free) 11th ” Polypetalæ (petals distinct) Epipetalæ (petals epigynous) 12th ” Peripetalæ (petals perigynous) 13th ” Hypopetalæ (petals hypogynous) 14th ” Diclines, flowers unisexual, or without a perianth. 15th ”
This system, being likewise founded partly on individual organs, is also, to a certain extent, artificial; and, strictly speaking, every natural method of botanic classification must partake more or less of an artificial character, as many orders of plants merge so insensibly into others that their respective limits cannot be accurately or rigorously defined.
FOOTNOTES:
[37] Carpenter on the Microscope.
LIV. ZOOLOGY
CLASSIFICATION OF ANIMALS—VERTEBRATES AND INVERTEBRATES—PROTOZOA—HYDROZOA—ACTINOZOA.
Zoology treats of life—of organized beings which are capable of voluntary motion. Plants exist, animals live and move. Both are organic beings, but the latter possess the faculty of will and spontaneous movement. The animal can leave a place and enjoy other surroundings, the plant cannot. We have already crossed the borderland which connects the plant and the animal. We have seen plants almost animals. We could commence this section with animals which are almost plants, so closely do the divisions approach each other. ZOOLOGY is the science of the knowledge of animals as BOTANY is of the knowledge of plants.
Where there is vegetation there are animals, not quadrupeds or bipeds necessarily, but numbers of small, it may be invisible, creatures which exist upon the vegetable kingdom—the algæ and minute creations of globules and cells, the infusoria already mentioned, the corals, etc. And in the “protozoa,” or first specimens of animal life, we have a similarity to the vegetable kingdom; we then get by gradual steps to other more perfect beings, each after his kind, till we arrive at the most perfect animal—MAN.
Animals are divided into two families, the INVERTEBRATE and the VERTEBRATE. The former has no spine nor skeleton; the latter has both. These again are divided into sub-families, classes, and orders, as follows.
Man is an animal—but what is an animal? We can scarcely tell in a few words. Linnæus defined the difference between the animal and the plant, for the former, said he, live, grow, and feel, while the latter live and grow. We have protozoa in the animal kingdom consisting of a single cell or blood corpuscle, some others without mouths or digestive organs, some have no head; some, as in the tape-worm, only a so-called head, with suckers or attachments, after which it develops joints, which are at first imperfect, but gradually mature as they are pushed farther away by new-issuing joints.
Animals, therefore, do not all possess organs, nor is there any common organ by which all animals can be classed. The indispensable in one is absent in another, and while our mouths and digestive apparatus are all important, in other animals suckers and no digestive apparatus at all is quite sufficient. Some have one mouth, some several; some have mouths and a proboscis to assist them, some only the trunk and no mouth—so called—at all, as in some insects.
The organisms which could not be distinguished from vegetables were termed zoophytes, or plant animals, and, were space available, a comparison might be instituted between the extremes of growth of the animals and plants, from the largest whales to the tiny microscopic protozoa, and from the mould upon jam to the gigantic trees of California, one leaf of which it is said will shelter twenty men from rain.
Cuvier spent many years in perfecting his systematic arrangements of animals, and this classification, though many rearrangements have been made as modern discovery progressed, may be regarded as the fundamental system of all. Professor Agassiz adopted it with modifications. Professor Nicholson has made a somewhat different arrangement, but essentially there will be found but slight difference between them. We append both these arrangements for comparison:—
AGASSIZ-CUVIER.
INVERTEBRATA.
BRANCH I.—RADIATA.
Class I.—Polypi 2 orders Including actinoids and halcyonoids. ” II.—Acalephs 3 ” hydroids, discophoræ, ctenophoræ. ” III.—Echinoderms 4 ” crinoids, asteroids, echinoids.
BRANCH II.—MOLLUSCA.
Class I.—Acephala 4 orders bryoza, brachiopods, tunicata, and lamellibranchiata. ” II.—Gasteropoda 3 ” pipteropoda, heteropoda, and gasteropoda (proper). ” III.—Cephalopoda 2 ” tetrabranchiata, and dibranchiata.
BRANCH III.—ARTICULATA.
Class I.—Worms 3 orders trematods (including leeches, etc.), nematoids, and annelides.
” II.—Crustacea 4 ” rotifera, crinopods, tetradecapods, and decapods.
” III.—Insects 3 ” myriapods, arachnoids, and insects proper.
BRANCH IV.—VERTEBRATA.
Class I.—Myzontes 2 orders myxinoids and cyclostomes.
” II.—Fishes proper.
” III.—Ganoids 3 ” cælacanths, axipenseroids, and sauroids.
” IV.—Selachiens 3 ” chimæræ, galeodes, and batides.
” V.—Amphibians 3 ” cæciliæ, ichthyodi, and anoura.
” VI.—Reptiles 4 ” serpents, saurii, rhizodontes, and testudinata.
” VII.—Birds 4 ” natatores, grallæ, rasores, and incessores.
” VIII.—Mammalia 3 ” marsupiaia, herbivora, and carnivora.
In the vertebrated animals the blood is red in consequence of the minute cells (corpuscles) which contain the colouring matter. In invertebrate animals these red cells are absent, and so the animals are white-blooded. Some animals, again, are cold-blooded like the fish; birds and mammalia have warm blood. It is worthy of remark that the higher we advance in the scale the fewer the offspring of the animal. The animalcules multiply at the rate of many billions a day, and even one codfish is stated to contain more than nine millions of eggs. A mackerel will produce 500,000; and so on, as we rise, we find mammals with seldom more than ten young at a time, down to one single offspring.
We could fill pages with the account of the differences existing between animals created for such different purposes and fitted to inhabit different climates, their mode of feeding and catching prey. The manner of bringing forth and rearing the young, and the temperament and temper of the animal creation would fill a volume, but we cannot now stay to examine these various characteristics. The following is the arrangement now usually adopted:—
NICHOLSON.
INVERTEBRATES.
PROTOZOA.
The lowest forms of animal life—microscopic animals.
Gregarinida Cell forms; worm-like. Rhizopoda Amebæ, foraminifera, radiolaria, sponges. Infusoria. Suctoria, ciliata, etc.
CÆLENTERATA (THE OLD RADIATA).
HYDROZOA.
Intermediary, having a mouth and receptacle separated by no alimentary canal.
Polypes and Zoophytes, Actinozoa. Medusæ, millipores, corals, sea-anemones, tubipora, siphonophera, etc.
ECHINODERMATA.
Star-fishes, sea-urchins, sea-cucumbers, and crinoids.
ANNULOSA.
Entozoa Tape-worms, etc. Rotifera Wheel-Animalculæ. Annelida Worms, leeches. Cerripida Barnacles. Crustacea Shell-fish. Insecta Various insects. Arachnida Spiders, scorpions, etc.
MOLLUSCA.
MULLOSCOIDA—POLYZOA.
Acephala of headless pupa.
Tunicata Brachiopoda Lamellibranchiata (bivalves).
Encephala with head.
Pteropoda. Gasteropoda (univalves). Cephalopoda, cuttle-fish, etc.
VERTEBRATA.
ICHTHYOPSIDA.
Class I.—Fishes Various orders. ” II.—Amphibia Frogs, toads, salamanders, etc.
SAUROPSIDA.
” III.—Reptilia Tortoises, smaller snakes, lizards, etc. ” IV.—Birds Various orders.
MAMMALIA.
Class I.—Non-Placental Marsupials. ” II.—Placental Edentata, cetacea, ungulata, quadrumana, bimana, etc.
We will adopt the latter order as being the more modern, and endeavour to make the various classes of the invertebrates clear to the mind, if we cannot present them to the vision, of the reader.
In our sketch of Botany we remarked upon the similarity existing between the cells of plants and animals, and although there are, of course, differences, there are many points of resemblance in these cells.
Plants have their lowest representatives called Protophytes. Animals which correspond to this class are termed Protozoa, from the Greek, proton, first, and zoön, animal. The former are, as already mentioned, seen amongst the algæ, consisting of simple cells, and protozoa cannot easily be distinguished from them except in the matter of nutriment, for some protozoa have no mouth except in the infusoria class. The cells are very much alike, and Dr. Carpenter sums them up briefly as follows:—
“The animal cell, in its most complete form, is comparable in most parts of its structure to that of the plant, but differs from it in the entire absence of the ‘cellulose wall’ or of anything that represents it, the cell-contents being enclosed in only a single limitary membrane, the chemical composition of which, being albuminous, indicates its correspondence with the primordial utricle. In its young state it seems always to contain a semi-fluid plasma, which is essentially the same as the protoplasm of the plant, save that it does not include chlorophyl granules, and this may either continue to occupy its cavity (which is the case in cells whose entire energy is directed to growth and multiplication), or may give place, either wholly or in part, to the special product which it may be the function of the cell to prepare. Like the vegetable cell, that of animals very commonly multiplies by duplicative subdivision, it also (especially among protozoa) may give origin to new cells by the breaking up of its contents into several particles.”
The protozoa are microscopic creatures consisting of one or more cells, and are infinitely little, thousands existing in a drop of water. They have no distinction of sexes, and their generation takes place by subdivision or blending of cells. The infusoria are the highest of the protozoa, and were formerly included amongst the radiata. Their numbers are infinite, and in a drop of water (see fig. 828) some very interesting specimens will be found. These infusoria are merely sarcode, or a jelly-like substance, and some have cilia, or hairy appendages, with which they agitate the water and cause a kind of current which brings them food. It is this partaking of food which has served to divide the lowest animal from the lowest vegetable creations. There is no progressive increase of development from the lowest plant to the highest animal. The animal begins by himself, as it were, as the plant, and both grow up in different directions. The protozoa exist upon organic substances, while plants absorb inorganic substances and assimilate them.
The Gregarinidæ are very tiny cells, and though microscopically minute, they sometimes develop into worm-like or elongated oval bodies. They inhabit the intestines of crustacea, worms, and cockroaches, as well as of higher animals. They are capable of certain motion, but are not furnished even with the “false feet” (pseudo podia) of the rhizopoda, the next animal in these very low scales of creation.
Of the Rhizopoda the AMEBÆ are very interesting, and we find them in our veins as well as in the stagnant green water of the pond. They are simply sarcode or jelly, and, as the name implies, the amebæ can change their appearance (amoibos, changing). They possess a kind of crawling, progressive motion, and under the microscope will be perceived to develop a tiny bud, as it were, which is the “false foot” that assists its progress. These amebæ are in our blood moving about, and are always altering their form, and when warm they move more quickly in the red blood corpuscles or cells, but excessive heat will kill them.
These curious creatures feed by the foot they protrude; and by drawing in the “process” as it is termed, they can collect within themselves the nourishment they require. Of course they have no mouth, and if we can conceive a creature of this kind which thrusts out from a jelly-bag a tiny lump, and pulls it in again at any time and place it likes, we have an idea of an ameba.
The pond ameba is somewhat different from the others, inasmuch as it possesses an outer and inner portion or layer which are different in density. There is what is termed a contractile vesicle which “beats” as a heart beats, but this is very primitive. There is really no structure whatever in these rhizopoda, and, as we have seen, their shape is always undergoing change. The outer and inner layers of the amebæ are called “the ectosarc” and “endosarc” respectively; the latter contains the darker portion—the nucleus.
The Foraminifera have already been mentioned in the chapters on Geology. We find these minute creatures must have had a great deal to do with the building up of rocks, as they have the power to make tiny coverings for themselves, which have been built into rocks by the addition of sandy particles, and consolidated by pressure. Here we have a most wonderful instance of the tiniest creatures producing the greatest masses of the earth. The body is merely sarcode, the shell is carbonate of lime. The foraminifera produce false feet in abundance, which surround the cell like fine hairs or rays. They live in the sea, and when they die the shells descend upon the ocean floor, where they undergo many changes and become converted into rock. The ooze of the great oceans is composed of these shells, and is practically a chalky deposit; the shells are being built up as in former ages with the curious nummulites of the Eocene formation, which are amongst the most interesting of fossils.
SPONGES. We must go on at once to the Sponges, which form such an interesting subject as they are so familiar to us all. Sponge is not often regarded by the public as an animal, and though perhaps authorities may not have yet concluded in what category they should be placed, we may consider them here according to the list.
We find the spongida both in fresh and salt water, and they have given rise to much discussion as to whether they should be classed as animals at all. But that question having been finally settled, we can proceed to examine a sponge in its native state, and we shall find both skeleton and “flesh.”
The skeleton is hard and composed of needles of “tiny” texture. The flesh is “sarcode,” and the animal possesses no mouth, but is full of holes (pores) and canals through which the water is continually distributed. The outer layer of the sponge is formed of ultimate components of the living substance of the sponge (like the amebæ we have been considering). Each contains a nucleus, and when joined together form the outer layer of the body. Beneath is a wide cavity communicating with the exterior by means of minute holes, and filled with water. The cavity separates the superficial layer from the deeper substance, which is of the same character. In the water passages of the sponge are cilia which induce a cement, and the interior canals develop into chambers lined with sponge particles, and the water carries particles to the sponge, which represents a kind of sub-aqueous city, where the people are arranged about the streets and roads in such a manner that each can easily appropriate his food from the water as it passes along.[38]
Sponge, then, is a mass of living organisms—tiny living creatures capable of feeding and of movement, resembling amebæ or perhaps infusoria, with cilia, to enable them to obtain nourishment by a kind of inhalation or respiration. They are reproductive by sexual and a-sexual processes which produce spongellæ. The living sponge is a beautifully coloured animal, and grows upon almost any solid foundation; and in the autumn the parent sponge displays a number of yellow dots or “gemmules,” which are the young. These are soon cast off and left to shift for themselves, and seek their fortunes, helpless as they appear, in the wide and stormy sea. At last they find a resting-place, and fix themselves for ever, growing up and reproducing their species until they are carried off to be sold and used in civilized countries for domestic purposes.
We must leave these curious animalculæ and glance at the INFUSORIA, which constitute a higher branch, but microscopic and universal, and include those called Flagellate, Ciliate, and Tentaculate. The first have whip-like cilia, or feelers, or filaments, which are ever in motion to cause a movement of the water and carry food to the animal. You will find plenty of infusoria in any stagnant water, and when placed under the microscope a mouth may be perceived, but no stomach, nor any apparent receptacle for food, which appears to enter at once into the body substance. The other kinds capture their food by seizure by the tentacles, or by agitating the cilia, like the flagellata, and thus whipping the nourishment towards the mouth, as children will draw in a toy boat to land by agitating the water in the given direction. These cilia, or hairs, serve for organs of locomotion as well as of capture. These creatures are called Infusoria, because they exist in vegetable “infusions” exposed to the atmosphere.
Decaying vegetable or animal substances, such as the leaves of trees, grass, a piece of flesh, etc., affused with water and exposed to air and warmth, will speedily, upon microscopic examination, be found peopled with numbers of most active minute creatures of the most varied forms. These animalcules are found also in the stagnant pools around our cities, in the waters of rivers, harbours, and lakes, and even in the ocean.
In reference to the origin of these animalcules, the view was long entertained that they were generated spontaneously, that the decaying vegetable and animal substances were decomposed and resolved into these simple beings. More accurate experiments have shown, however, that the infusoria are produced from ova, or germs, which are probably carried about in the dried-up state, in the form of minute particles of dust,[39] ready to develop themselves in any spot which may afford them the requisite moisture and nutriment. In this respect they resemble the microscopic fungi, whose germs are diffused in the same way. When once they have obtained the means of development, they multiply with incredible celerity. If the decaying vegetable or animal substances be carefully excluded from contact with the air, or if the air be heated before it is admitted to them, no infusoria will appear. They are rarely developed on mountains of a certain height, where the atmosphere is free from foreign bodies.
Though these animalcules are so exceedingly minute, yet the forms exhibited by them are extremely various, and some of them present also considerable variety in the forms assumed by the same individual under different circumstances. In many species the soft body is enclosed in a firm integument, strengthened by a deposit of siliceous matter; these envelopes, which are often preserved after the death of the animals, are termed the shields, and the animalcules encased in them are called loricated infusoria. The remarkable discovery has been made that large distinct beds of former formations are entirely made up of the accumulated remains of these animalcules.
We arrive at the HYDROZOA after leaving the Infusoria, and find ourselves in the sea, and far from land, where it will be difficult for us to ascertain the characteristics of these interesting animals. But fortunately we can obtain much nearer home, and occasionally in a private aquarium, a specimen of the hydrozoa which will serve our purpose, as it has served before to introduce readers to the study of these water-polypes, some of which are so like plants that they are frequently mistaken for them.
The hydrozoa present a “definite histological structure,” says Professor Huxley; “the body always exhibits a separation into at least two distinct layers of tissue, an outer and an inner.” The Hydras, or fresh-water polypes, which may be found in nearly every pond adhering to the duckweed, appears like tubes, and if touched will curl up into tiny knobs. But if let alone they will adhere to a glass by their single foot, or sucker, which can be moved at pleasure.
The foot, or sucker, is continued to a slender cylindrical stalk, from the end of which radiate a number of tentacles, or “feelers,” growing around the mouth, and serving to convey or attract food to the animal which is, so to speak, all stomach. There is no breathing apparatus, and what food it cannot digest is expelled from the mouth. The peculiarity which has given the hydra its name is, that no matter into how many pieces you cut this polype, the parts cut off will all develop into little polypes perfect as their parent.[40] But germination is carried on naturally by buds thrown out, and cast (by “gemmation”), or by the ordinary sexual production of ova.
The outer and inner skins of the hydra are called the ectoderm and endoderm, and the animal is quite capable of locomotion, walking, or rather moving, backwards, by raising and planting its sucker or foot, and by swimming. The prey is captured by the tentacles and by the darting out of tiny spears from the cells or “thread cells” which contain them on the surface of the body. The well-known “Portuguese man-of-war,” an ocean polype, has these “harpoons” greatly developed, and can inflict serious pain as of many stinging nettles; the sensation is exceedingly painful, and lasts some time.
The MEDUSIDÆ are known to the seaside visitor as the jelly-fish, and the other Acalephæ, the “hidden-eyed” medusæ, include the Portuguese man-of-war mentioned above, and many other umbrella-like animals. They have received the name of medusæ from Medusa, whose long, snaky locks the tentacles of the animals are supposed to be like. Some of these “floating umbrellas” are very dangerous, and will inflict severe stings upon any one in their vicinity. The tentacles or filaments extend for a long distance, and bathers should be cautious. We have often watched them, and they are beautiful to contemplate particularly at night, and in Kingstown Harbour, near Dublin, many exceedingly fine specimens have been obtained. The pulsation of the “umbrella” or bell, enables the animal to swim, and the even undulations of this beautiful covering are apparently caused by nervous contractions.
The jelly-fish have no resemblance to “fish,” and scarcely appear to exist; they are of no use to man, and when removed from the water dwindle by little and little to a tiny film and nothing more—they dissolve into air and water. Cases have been known and tales told of how farmers collected hundreds of these jelly-fish for manure, and when the cart reached the field, to the man’s astonishment, nothing was left but what appeared cobweb in the place of the load of fish.
The Cyclippe is a very common specimen, and moves by means of its cilia; Cestum Veneris—the zone or girdle of Venus—is another curious example. It appears like a glass ribbon about five inches wide and perhaps four or five feet long. The cilia when in motion are very brilliant in colouring, and the creature undulates through the water in a remarkable manner.
The luminosity of the medusæ is clearly perceived, the so-called phosphorescence being due chiefly to the minute jelly-fish which abound near the surface of the sea. It appears impossible, for most, at any rate, if not all, these medusæ to sink beneath the surface, for they can be found in hundreds cast ashore, melting away into film. We might imagine that they would be provided with some means of sinking themselves, but being apparently only air and water, it is necessary for them to remain upon the surface to exist at all.
The term Acalephæ, by which they are known, means “stinging” fish or sea-nettles, the Greek word meaning nettle.
The ACTINOZOA comprise corals and the popular sea anemones (actinidæ). They resemble the hydrozoa in possessing tentacles, and also the two inner and outer tissues of the body. But they differ from the hydrozoa in their interior arrangement in the possession of a kind of stomach between the “body cavity” and the mouth which the hydrozoa do not possess. The appearance of the sea anemone is well known. It fixes itself by the flat base and hangs out its tentacles to obtain food. When we touch an anemone with a stick we perceive how it contracts itself, but there is no nervous system nor any respiration. The reproduction of its species is carried on within, not as in other animals, like the hydra, by exterior budding.
The corals belong to the same class as the sea anemones, and are called zoanthidæ. We have already in previous portions of this volume mentioned the “coral” building polypes, but we may again describe them here. We have the black coral or antipathidæ, which live in masses and are united by a stem. They grow upon this fleshy trunk and cover it in time “just as a trunk of a tree is covered by the bark.” This stem is called a cænosarc, which secretes the coral, or skeleton. The madrepores are the greatest producers of the coral of commerce.
“If we examine a simple coral of this group,” says Professor Nicholson, “we find that we have to deal with an animal in all important respects identical with an ordinary sea anemone, but having a more or less complicated skeleton developed in its interior.” This skeleton is the corallum, and it is composed, as most people are aware, of calcareous matter deposited within the polype itself; in the former case the development or formation is exterior to the polype. A single polype will thus secrete a deposit, and a colony of them produce a compound skeleton, and as they throw out buds or young polypes, the manufacture of skeletons goes on by secretion.
The Tubipores are like pipes, and the coral has been termed the “organ-pipe.” It is formed cylindrically and joined externally. As under GEOLOGY we have examined the question of coral reefs, we need not here recapitulate the descriptions given in that section.
Doctor Bariel writes of these animals as follows:—“By far the greater part of the Zoanthoid polypes, as they grow, deposit in the cellular substance of the flesh of their back an immense quantity of calcareous matter which enlarges as the animal increases in size, and, in fact, fills up those portions of the substance of the animal, which by the growth of new parts are no longer wanted for its nourishment, and in this manner they form a hard and strong case, amongst the folds of which they contract themselves so as to be protected from external injury, and by the same means they form for themselves a permanent attachment which prevents their being tossed about by every wave of the element in which they live. The stony substances so formed are called corals, and their mode of formation causes them exactly to represent the animal which secretes them. The upper surface is always furnished with radiating plates, the remains of the calcareous particles which are deposited in the longitudinal folds of the stomach.”
FOOTNOTES:
[38] Huxley. “Classification of Animals.”
[39] That the presence of millions of such ova in the air should not be detected, will appear very natural indeed, if we reflect that the animalcules are only 1/1500 to 1/2000 part of a line in diameter, and that the ova are a thousand times smaller.
[40] Hercules conquered the “Hydra,” which is represented in mythology as capable of reproducing two heads for each one cut off by the warrior.
LV. ECHINODERMATA—ANNULOSA—ENTOZOA—INSECTA
SEA-URCHINS—STAR-FISHES—FEATHERY STARS—SEA-CUCUMBERS—WORMS—LEECHES—ROTIFERS—TAPE WORMS—INSECTS.
The ECHINODERMATA or spiny-skinned, are most commonly represented by the sea-urchins and star-fishes of our coasts. In some of the classes locomotion is performed by means of these spines or prickles, which serve as legs. In others, movement is carried on by suckers and tubes as in the star-fishes, these tubes being also the means whereby the animal obtains its food.
They have a digestive system, and possess a curiously horny skin even when spines are absent. The mouth is in the centre. We give an illustration of the sea-urchin, and of a section of a spine, which is a beautiful object when seen under the microscope, for these spines can be made quite transparent when cut across and ground. The shelly covering is porous, and as the animal grows the shell is added to at the edges. Underneath will be found the mouth, which has teeth fitted for devouring the small crustacea. These sea-urchins abound, and their porous shells may be picked up frequently after a storm.
The star-fishes are well known to all searchers amongst the rocks and those who study the shore, and are often taken home for an aquarium. They are very voracious, however, and when one is examined in a glass of sea-water, the observer will detect many suckers protruding from each of the rays. It is by means of these suckers, which are put forth from innumerable little holes called “ambulacral apertures,” that the star-fish makes his way up the rocks and along the ocean bed. The stomach of the star-fish is extensive, and situated in the centre of the rays wherein is a digestive apparatus. The rays are composed of detached but beautifully fitted pieces, so united as to be flexible, and around the mouth and in strong frame-work. The star-fish has no teeth, but manages to dispose of a vast quantity of matter, which if left alone would be injurious in decay.
Thus Nature has provided a shore scavenger to devour what would be harmful, just as the vulture on land eats the carrion. Besides this kind of refuse food, the star-fish eats small crustaceans, and oysters fall victims to him. By embracing the shell the star-fish manages to insert itself, and if it cannot bring the oyster out to its mouth, it will quietly turn out its mouth into the oyster-shell, and save the bivalve any trouble in the matter. Some writers declare that the star-fish stupefies or poisons its victim, and then the shell opens. These asteroidea can reproduce a ray that has been injured or cut off, or they can break themselves to pieces if caught.
The brittle stars and feather stars appertain to the order of the Ophiuroida or “serpent-armed,” because the rays are more flexible and thin than the common star-fish. But they differ very much from the star-fish in the arrangement, as well as in the shape of their arms. The former possesses rays which form an appendage of the stomach and enclose it. In the brittle stars the rays are limbs, and could be detached without taking the life of the animal, except in so far as to deprive it of means to obtain its food. The body is quite independent of the rays, the mouth occupying the centre, and is surrounded by minute suckers. The stars are much more flexible than the star-fishes, their rays are longer, and serve either as feet, fins, tentacles, or arms.
The crinoids also belong to the Echinodermata, and resemble plants more than star-fish. They are fixed upon a stalk like a flower, growing upright from the sea-bottom, and the body is called a calyx, which is composed of a ventral and dorsal surface. The arms branch out from the calyx, just as a small tree does, and if we can imagine one of the last planted trees on the Thames embankment reduced to half a finger’s length or less, we have a sort of idea of the crinoid “in the rough.”
A polype supported on a stem branching out in feathery, grassy-looking arms represents the Encrinites, the remains of which are found as fossils. The arms of the crinoids are subdivided, and quite a flowery crown may in time result. The animal obtains its food by the motion of cilia. The stem and the branches are jointed, as it were, and capable of flexible movement in any direction. The crinoids remain stationary during their lives.
The care taken by the star-fish of its young is remarkable. It carries the eggs about in its suckers and with great caution. The young remain attached to the mother until they are able to go about alone, and then the physical attachments die off, and the asteroidea goes forth to seek its fortune in the sea.
The echinus, already mentioned, is a most elaborately constructed animal; the plates being secreted from the soft parts are ever being renewed as the animal gets older and larger. The whole subject is well worth a long independent study, of which it is here impossible for us to give the results.
The sea-cucumbers are more like the familiar garden slug than any other animal, and are surmounted by a fringe round the mouth which looks like leaves. The surface is moist, and has no horny covering like the “urchin,” or star fish, but the suckers are present and are used for locomotion. The tentacles round the mouth serve as prehensile organs. The “alimentary canal” is most curiously curved, and of great length, and the animal can turn itself “inside out” with great facility if alarmed. It possesses a kind of breathing apparatus, and may be classed as the most highly organized of all the Echinodermata. These cucumbers are much esteemed by the Chinese, and “trepang,” as they are called, are caught by thousands in Australian waters.
ANNULOSA.
The worm-like animals are divided into sections, which include intestinal worms, entozoa, annelida, and crustacea, with the worms, spiders, and insects classed in each section. We may at once perceive what a very extensive division the Annulosa is, and we must devote some space to it.
The Rotifers, or “wheel animalculæ,” are included in this class; they stand almost alone, and certainly invisible to the naked eye. They are very curious animals, as will be seen from the accompanying illustration. The motion of the cilia around the mouth gives the whirling movement from which their name is derived (fig. 841).
The ANNELIDES, or worms, include earth-worms, water-worms, leeches, etc. The appearance of the earth-worm is so common that few people comparatively studied it until Mr. Darwin’s book took the amateur reader by surprise and delighted him, and to that volume we must refer our readers for details of these very interesting animals, termed annelides because of the rings appearing upon their bodies.
The common leech is well known in medicine. It is curiously enough an inhabitant of ponds and lakes, and in such conditions has no opportunities for tasting the warm blood for which it develops such a liking when opportunity offers. This is really a remarkable fact, that the animal should be placed in a position naturally in which its most natural tendencies should remain unsatisfied.
The progression of the leech is performed by undulating movements and the prehensile action of the suckers—head and tail. The eyes are ten in number, near the mouth and at the top of the head. The mouth is furnished with numerous tri-radiate teeth, but in some leeches they are not sharp, as in the “medicinal” variety. It is known that both sexes are represented in every leech, but they are not self-reproductive.
The earth-worm, so familiar to all, has been lately raised into importance. It lives in clay, and bores its way through the ground. It feeds upon organic matter contained in the earth, and when it has assimilated the nourishing particles, it ejects the remainder in small heaps of soft dirt, which are visible after rain particularly. The worm, by its burrowing, turns up the land, and vastly increases its fertility.
The earth-worm in its outer structure resembles the leech, but, as any one will at once perceive, the worm is not furnished with suckers by which it can assist itself to move. Instead of these rounded terminals the worm is finely pointed, and thus capable of boring its way through the earth. Progression is accomplished by moving first the head portion and then the next, so that a regular series of movements is necessary. The minute spines or bristles of the worm prevent its body being retracted by muscular effort.
The vital organs are rather forward of the centre of the body, and so if a worm be cut behind them it will survive and reproduce a tail. But the portion cut off will not be found alive, nor is it capable of forming a new perfect worm as generally supposed.
There are many other orders of worms which we can only indicate—viz., the Tubicolæ which surround themselves with a hard case; the Errantia, or sea-worms, sand-worms, etc., like the lobworm used for bait, and the naiads of our fresh-water ponds, all of which are suited to the aquatic life they lead. Indeed, of all the annelides, the earth-worm is the only specimen that is suited for living upon land. As regards the last mentioned, we may add that worms do not prey upon dead bodies as is so generally imagined. They are vegetable feeders, and do not burrow very deeply.
The transparent condition of the Rotifers renders them easy of observation under the microscope, and we find a nervous system, intestines, and a developed stomach. They are fresh-water inhabitants.
The Entozoa or “intestinal” worms claim a brief notice at our hands. The entozoa are those beings which inhabit, as parasites, the intestines and other parts of animals. Their history is still obscure, but there seems to be about twenty varieties of these creatures, and a great number of animals have their peculiar entozoa. The best known in the human subject are the “Ascaris” or thread-worm, the “Lumbricus Teres” or long-worm, and the “Tænia” or tape-worm; this last is jointed, and grows to several yards in length.
The development of these Tænia is one of the most curious performances of nature. Each of the joints shown in the illustration below (fig. 842) is a perfected and mature proglottis, containing the ova or eggs, which can only be brought to perfection when swallowed by a warm-blooded animal (not the same from which they emanated). The head within the embryo then holds to the tissues and penetrates to the alimentary canal, where only it can redevelop joints from the so-called head, which has no organs and merely pushes out immature joints which are continued, and they become more mature the farther they are pushed out by the new ones. The “measles” of the pig are produced by the ova of these worms.
MYRIAPODA.
The “many-footed” annulosa include the centipedes and millipedes, and may be regarded as a connecting link between the worms and the insects. The heads of these animals are distinct from the body.
The millipedes can be any day found under a large stone in a field which has not been tilled, or any place where a stone has been suffered to remain for some time undisturbed. These specimens are of the pill-millipede order, because they roll themselves up into a ball when disturbed. The myriapods of this country are not of large dimensions, but in tropical climates they attain a great size. The giant centipede has been found in South America more than a foot long, and is capable of inflicting severe wounds, its tenacity being extraordinary and equalling that of the bull-dog when once it has gripped its enemy.
The myriapods have no wings; they possess antennæ, and numerous, never less than eighteen, feet,—frequently twenty pairs, but never a thousand, much less “ten thousand” feet, as the class name indicates. They are provided with strong forceps or “foot-jaws,” which supply a poison for killing their enemies. The millipedes and centipedes are known scientifically as Iulidæ and Scolopendridæ respectively, and in most points of internal arrangement resemble insects, such as breathing by spiracles or (stomates), and trachæ or tubes. Some of the centipedes possess electric qualities, and can administer a shock to an opponent.
INSECTA.
Insects inhabit the world around us in myriad forms in air and earth and water. Some exist for a very brief space in the air; others live under water, or in trees, or in the ground; some burrow and hide in chinks of rocks and under stones. The numbers are countless, and all have some function to perform as palpably as the busy honey-bee, or as mysteriously as the giddy, careless butterfly.
Insects are divided into three distinct parts,—viz., the head, the thorax, and the abdomen, and each of these parts has a pair of legs attached to it, as will be perceived from the accompanying diagram. Along the body are tubes called trachæ,—for insects do not breathe by lungs,—by which the air is carried into the system of the insect, by the “spiracles” or openings of fine network, to prevent dust entering the air-passages. The head is joined to the body by a constricted neck, the part of the body to which it is joined is called the thorax, and to this is added the posterior part or abdomen; this part is extremely various in form in different insects; in some it is round and full, in others long and extended. The antennæ arise from the head, and are generally composed of eleven pieces variously disposed; these wonderful organs are possessed of great sensibility, and they certainly serve to convey information to the insect, of the nature of one of the special senses; it was formerly thought to be simply that of touch very much refined, or of smell, but it is now generally considered to be that of hearing, or a modification of it. The forms of the antennæ are very various; fig. 845 represents that of the cockchafer (Melolontha vulgaris). The legs proceed from the thorax as do the wings, the abdomen giving rise to none of the extremities; the feet of insects are all pretty much upon the same model, some being more developed than others, they have a pair of hooks or claws for catching and clinging to rough surfaces, and a pair of cushions or pads, covered in some cases with suckers.
The foot of the common house-fly is most beautifully fitted for its progression and support. We have often wondered how the fly manages to support itself back downwards on the ceiling, or walk up glass. We give a cut of the fly’s foot (fig. 846).
The eyes of insects are also marvellous. There are only two, but each one is composed of numerous cells (ocelli), and look like a honey-comb. (See illustration, fig. 847.)
Insects swarm in innumerable companies, and no one who has not seen the locusts descending upon the earth can form more than a faint idea of the devastation they occasion in an incredibly short time. These, as well as thousands of other insects, exist in myriads, and we must content ourselves, on this occasion, by merely noting the different orders and their characteristics, after we have mentioned some of the attributes common to all.
The term “insect” means cut into or divided, and so the insecta are divided, as already mentioned, into three parts,—head, thorax, and abdomen,—the thorax being subdivided into three rings, pro-thorax, meso-thorax, and meta-thorax—beginning, middle, and end. All insects have six legs, and usually two or four wings, though some have no wings at all. The legs are united to the thorax, the antennæ and eyes to the head. The abdomen contains the important sexual organs, a sting or defensive weapon, and in females the egg chamber.
Insects breathe by tubes in the sides, and consume a great quantity of air. Their powers of flying and leaping are too familiar to need dwelling upon. The wings display beautiful colours like those observable in the soap-bubble, others are covered with scales or hairs. The mouths vary very much with the species, as the manner of obtaining food is by suction or gnawing. The blood of insects is pale and thin.
The various transformations which insects undergo are always a subject of interest for the young student. The ugly forms which develop in beautiful creations are more astonishing than the change of the “ugly duckling” into the graceful swan.
Insects come to maturity only after undergoing successive changes from the egg to the perfect animal. The eggs (some of which are very beautiful) are first deposited in some safe place, either attached to a leaf or tied up in a small bundle by silken threads spun by the parent insect, and in some nutritious substance, so that when it comes to life it may at once have food; this is sometimes in manure, sometimes in flesh, and sometimes under the skin of a living animal (few are exempt from this infliction), where they remain for a time and then come forth as maggots, caterpillars, etc.; in this state they are called larvæ,—these are generally active creatures and eat most voraciously, which seems to be the principal act of this state of their existence. These larvæ frequently change their skins as they grow, and at last they assume the next stage of their life, the pupa or chrysalis state, which is one generally of complete inactivity; many of these larvæ weave themselves a covering of a sort of silk, to defend them while in the pupa state,—such as the silkworm, whose covering (cocoon) is the source of all the silk of commerce,—others merely place themselves in a situation of security. The pupa remains dormant for a certain time, and then becomes the imago or perfect insect (the last state of its existence), such as a moth, a butterfly, a beetle, etc. These are of different sexes, and in due time produce a batch of eggs and then die; these eggs are often incredible in numbers, amounting to many thousands—but few escape the watchful eyes of other insects and of birds who feed upon them.
But there are some of the insecta which do not undergo metamorphosis; the APTERA or wingless insects include these, as the flea and such parasites which bore into other animals, and deposit their eggs within them.
Insects have very little means for making themselves audible, at least so far as can be ascertained. The humming of bees and flies and other insects are, of course, not intended to represent the voice. The cricket’s “chirp,” as people commonly imagine, but the sound is attributable to the rubbing together of the wings or wing-cases, as is the noise produced by the field-cricket. There is a very peculiar sound attributable to the “Death-Watch,” a ticking, and to nervous people terrible warning of dissolution. It may reassure some one, perhaps, to know that this “unearthly sound” is caused simply by the insect beating its head against a piece of wood to attract its mate, as the female glow-worm lights her lamp to guide her lord to her bower.
The INSECTA may simply be divided into nine orders:—
1 COLEOPTERA. Beetle tribe. Case-winged. 2 ORTHOPTERA. Locusts, crickets, etc. Straight-winged. 3 NEUROPTERA. Dragon-flies, etc. Nerve-winged. 4 HYMENOPTERA. Bees, ants, wasps, etc. Membrane-winged. 5 STREPSIPTERA. Parasites of the foregoing. Twisted-winged. 6 LEPIDOPTERA. Moths and butterflies. Scale-winged. 7 HEMIPTERA. Bugs, water-boatmen. Half-winged. 8 DIPTERA. House-fly, gnat. Two-winged. 9 APRANIPTERA. Fleas, “chigos.” Wingless.
(Of these the metamorphoses of 1, 3, 4, 6, and 8 are complete).
The COLEOPTERA are well represented in England as beetles. They have four wings, but the outer pair serve as coverings to the inner ones. They are termed Elytra, and are horny in texture. These beetles are short-lived, but useful as scavengers, and serve to manure the ground by burying objectionable matter. The larvæ of beetles eat tremendously. The stag-beetle is a formidable-looking animal, and the lady-bird is well known as an enemy to the aphides on our rose trees. The tiger-beetle, cockchafer, and various water-beetles belong to this family. The scarabee, or sacred Egyptian beetle, also will be found classed with the coleoptera. Many of these beetles are excellent scavengers, and some called burying beetles remove the soil underneath the carcases of birds and other small dead animals, letting them fall down below the ground level; the beetles then lay their eggs in the body, so that sustenance may be at hand for the young when hatched.
The ORTHOPTERA include our cockroaches, miscalled “black beetles,” the locusts, crickets, etc. The ravages of the locust are well known. The larvæ of the orthoptera has no wings, but otherwise is very like the grown insect. They change their skins frequently before they become perfect insects.
Passing the “nerve-winged” dragon-flies and caddis, whose larvæ case is so familiar and useful as bait, we come to the very important and interesting order of HYMENOPTERA, with four membranous wings. In this rank we find bees, wasps, and ants, the first and last named being proverbial for industry and examples of almost superhuman reasoning powers, and a similitude to man’s arrangements in labour and house-building marvellous to contemplate. A study of the habits of ants, bees, and wasps will reveal a state of society existing amongst them which more nearly resembles man in feelings and habits, for these insects possess means of oral communication.
All these insects are armed with a sting, or other offensive weapon. The ant possesses the “formic” acid, which derives its name from the possessor. The destructive white ants will eat away a wooden house very quickly, sapping and mining it in all directions till it is a mere skeleton. The habits of bees are so well known and have been so often described that we need not detail them. The manner in which the ants “milk” the aphides is curious and interesting.
The STREPSIPTERA order includes very few species, so we may pass quickly to the LEPIDOPTERA, the butterflies and moths, whose beautiful colourings and markings have attracted us all from childhood. There are about 12,000 species of the lepidoptera, and they are divided into “moths” and “butterflies,” the former being seen in twilight, or darkness, the latter in sunlight. They can readily be distinguished by the antennæ, those of the butterfly being tipped, or knobbed. The silkworm belongs to this family. These insects undergo complete metamorphosis. The remaining two orders of insects include the house-flies and gnats; and the flea, and jigger, or chigo, which penetrates the skin and lays its eggs in the flesh, causing thereby dangerous inflammation.
CRUSTACEA.
This class includes a number of familiar animals such as the barnacle, the crab, the lobster, shrimp, etc.; and curious as it may appear are closely related to our spiders. Their cases or coverings are all articulated or disposed in distinct segments. They breathe through gills or by tubes, and possess legs, or appendages for walking, eating, or guidance. They are generally marine creatures.
The shell of the crustacea is composed largely of lime, and of course becomes very hard in time. It is formed from the skin. The body, like that of an insect, is composed of head, thorax, and abdomen, divided into twenty-one segments, of which seven occupy the head, seven the thorax, and the remainder the abdomen. Twenty segments are furnished with legs, or feelers, or claws—a pair to a segment. The lobster or crayfish will give excellent examples of the anatomy of the macrura or lobster kind of crustacea. The heart is situated in the back.
The following table given by Professor Nicholson will explain the “segments and appendages” of the lobster:—
{ 1st Segment, Eyes. { 2nd ” Lesser antennæ { 3rd ” Greater antennæ. Head { 4th ” Pair of biting jaws. { 5th ” First pair of chewing jaws. { 6th ” Second pair of chewing jaws. { 7th ” First pair of foot jaws.
{ 8th ” Second pair of foot jaws. { 9th ” Third pair of foot jaws. {10th ” First pair of legs (claws). Thorax {11th ” Second pair of legs (small claws). {12th ” Third pair of legs (small claws). {13th ” Fourth pair of legs. {14th ” Fifth pair of legs.
{15th ” Ground appendages. {16th ” Swimmerets. {17th ” ” Abdomen {18th ” ” {19th ” ” {20th ” Large swimmerets. {21st ” No appendages (tail fin).
The tail is, as may be supposed, the great aid to locomotion in the lobster family, and they can swim backwards with great rapidity by its assistance. Lobsters shed their claws when alarmed, and are easily caught by a glittering bait.
The hermit crabs are interesting creatures, but do not possess the horny coat of the crab or lobster. They are therefore compelled to inhabit an empty shell, into which they thrust themselves, holding to the bottom of it by their tail, while a large claw guards the entrance. When the animal gets too big for his house he moves to another, leaving the old home for another hermit of the shore.
The crabs have no developed tails, and are therefore called brachyura—“short-tailed,” and they are walking creatures. There are king crabs, land crabs, and the common swimming crab. These animals can shed their shells as other crustaceans, and a curious fact is they shed them whole. How the claws come out must remain more or less a mystery. Réaumur investigated the action of the crayfish, and noticed that as the casting time approached the crustacea retired to some hiding-place and remained without eating. The shell becomes gradually loosened, and at last by putting its feet against a stone and pushing backwards the animal jerks himself away. It must be a painful operation, for the mill-like teeth of the stomach are also rejected, and the joints do not give way. After a while a new shell appears, and is cast in due time as before.
The eyes of the crustacea are situated in front, and are composed like the insects, or are simple, like spiders. They possess a sense of hearing evidently. The eggs of the lobster are carried by the female, and they are termed the “coral” in consequence of their red and beadlike appearance. Our space will not admit of our saying much more concerning the interesting crustacea, though the barnacles, so well known by sight by all dwellers at the sea, and called Cirripedia, which fix themselves to rocks and ships, deserve notice. The young are capable of movement, and this fact was first discovered in 1830. It resembled a mussel, but when kept in sea-water it adhered to the vessel which retained it. The cirripedia are so called from the cirri or arms which they possess, and by which they are enabled to entangle or catch their food, as in a net. They hold themselves by a “foot stalk.” The goose-mussel, or barnacle, is very common, but must not be confounded with the limpet.
Dr. Baird gives the following description of them:—“The cirripeds are articulated animals contained within a hard covering composed of several pieces and consisting of calcified chitine. The body of the animal is enclosed in a sac lined with the most delicate membrane of chitine, which in one group is prolonged into a peduncle and contains the ova; the body is distinctly articulated and placed with the back downwards.
ARACHNIDA—SPIDERS.
There are many families of arachnida besides the well-known garden and house spiders. The sea spiders, though classed with the arachnida, are sometimes placed amongst the crustacea. We have the “tick” and the cheese-mite and the scorpions; all of which belong to the spider family. But the true spiders are known by the joining of the two upper segments, the thorax and head being united (cephalo-thorax). The pretty and marvellous webs are spun from abdominal glands through small apertures. The fluid hardens in its passage sufficiently to be woven into threads to resist the struggles of the captured prey. The forms of these webs vary, but some spiders do not catch their victims in the net; they pounce upon them cat fashion. The large house spider is well known to all. The garden spider is seen in the illustration (fig. 855) with the scorpion. The habits of spiders will be found a very interesting study, and many volumes have been devoted to them. The water spider is a frequent inmate of an aquarium, and the bubble of air he takes down with him to breathe serves as a means of living while he is seeking his aquatic prey.
We will close our rapid survey of the invertebrate animals with a glance at the MOLLUSCA, which are divided into six classes (see page 703). The first is the Tunicata, which have no shell or hard covering, and come under the denomination of molluscoids, and belong to a lower order. The true mollusca include the Brachiopoda, which have a pair of shells. They are called “arm-footed” because a long cord or tendon passes through one of the shells, and fixes the mollusc to the rock. The Lingula of this class have been discovered in very old formations such as the Devonian period, and indeed appear to have been amongst the first created animals.
The Lamellibranchiata include the oyster, cockle, mussel, etc. They are well known, and scarcely need description. The Pteropoda have no shell. The Gasteropoda are very numerous, and periwinkles, whelks, snails, etc., belong to this class. They progress by a muscular “mantle,” which is extended and contracted. The “horns” have eyes at the extremities. When they retire into their “houses” they can close the door by a kind of lid called the “operculum.”
The Cephalopods include the nautilus and the cuttle fish, the terrible squid, or octopus, etc. Wonderful tales are told of the tenacity and ferocity of the “Poulpes,” and no doubt in long-past ages these animals attained a gigantic growth. They are very unpleasant enemies, and the cold, slimy grasp of the long tentacles is apt to give one the “horrors,” while the terrible head and beak fill one with dismay. The poulpes are very formidable opponents, and discretion will certainly be the better part of valour when they appear in our vicinity.
We must here close our sketch of the Invertebrates, and we regret that the limits of our volume will not permit us to continue this interesting subject, nor can we find space, at present, for even the barest description of the Vertebrate animals.
LVI. THE ANALYSIS OF CHANCE AND MATHEMATICAL GAMES
MAGIC SQUARES—THE SIXTEEN PUZZLE—SOLITAIRE—EQUIVALENTS.
We will now proceed to draw our readers’ attention to several experiments very famous at a former period, but which our own generation has completely overlooked. We refer to the Analysis of Chance, a science still known under the title of Calculation of Probabilities, formerly cultivated with so much ardour, but to-day almost fallen into oblivion.
Originating in the caprice of the clever Chevalier de Méré, who in 1654 suggested the game to Pascal, the analysis of chance has given rise to investigations of an entirely novel kind, and attempts have been made to measure the mathematical degree of credence to be given to simple conjectures. We will first recapitulate the principles laid down by Laplace on this subject. We know that of a certain number of events, one only can happen, but nothing leads us to the belief that one will happen more than the other. The theory of chance consists in reducing all the events of the same kind to a certain number of equally possible cases, such, that is to say, that we are equally undecided about, and to determine the number of cases favourable to the event, whose probability we are seeking. The ratio of this number to that of all possible cases is the measure of this probability, which is thus a fraction, the numerator of which is the number of favourable cases, and the denominator the number of all possible cases. When all the cases are favourable to an event, its probability changes to certainty, and it is then expressed by the unit. Probabilities increase or diminish by their mutual combination; if the events are independent of each other, the probability of the existence of their whole is the product of their particular probabilities. Thus the probability of throwing an ace with one dice being 1/6, that of throwing two aces with two dice is 1/36. Each of the sides of one dice combining with the six sides of the other, there are thirty-six possible cases, among which one only gives the two aces. When two events depend on each other, the probability of the double event is the product of the probability of the first event by the probability that, that event having occurred, the other will occur. This rule helps us to study the influence of past events on the probability of future events. If we calculate á priori the probability of the event that has occurred and an event composed of this and another expected event, the second probability divided by the first, will be the probability of the expected event, inferred from the observed event.
The probability of events serves to determine the hope or fear of persons interested in their existence. The word hope here expresses the advantage which someone expects in suppositions which are only probable. This advantage in the theory of chances is the product of the hoped-for sum by the probability of obtaining it; it is the partial sum which should arise when one does not wish to run the risks of the event, supposing that the apportionment corresponds to the probabilities. This apportionment is only equitable when we abstract from it all foreign circumstances; because an equal degree of probability gives an equal title to the hoped-for sum. This advantage is called mathematical hope. Nevertheless, the rigorous application of this principle may lead to an inadmissible consequence. Let us see what Laplace says. Paul plays at heads and tails, on the understanding that he receives two shillings if he succeeds at the first throw, four shillings if he succeeds at the second, eight at the third, and so on. His stake on the game, according to calculation, must be equal to the number of throws; so that if the game continues indefinitely, the stake also continues indefinitely. Yet, no reasonable man would venture on this game even a moderate sum, £2 for example. Whence, therefore, comes this difference between the result of the calculation, and the indication of common-sense? We soon perceive that it proceeds from the fact, that the moral advantage which a benefit procures for us is not proportional to this advantage, and that it depends on a thousand circumstances, often very difficult to define, but the chief and most important of which is chance. In fact, it is evident that a shilling has much greater value for one who has but a hundred than for a millionaire. We must, therefore, distinguish in the hoped-for good between its absolute and its relative value; the latter regulates itself according to the motives which cause it to be desired, while the former is independent. In the absence of a general principle to appreciate this relative value, we give a suggestion of Daniel Bernouilli which has been generally admitted.
The relative value of an extremely small sum is equal to its absolute value, divided by the total advantage of the interested person. On applying the calculus to this principle, it will be found that the moral hope, the growth of chance due to expectations, coincides with the mathematical hope, when chance, considered as a unit, becomes infinite in proportion to the variations it receives from expectations. But when these variations are a sensible portion of the unit, the two hopes may differ very greatly from each other. In the example cited, this rule leads to results conformable to the indications of common-sense. We find, in point of fact, that if Paul’s fortune amounts only to £8, he cannot reasonably stake more than 7_s._ on the game. At the most equal game, the loss is always, relatively greater than the gain. Supposing, for example, that a person possessing a sum of £4, stakes £2 on a game of heads or tails, his money after placing his stake will be morally reduced to £3 11_s._ 0_d._—that is to say, this latter sum will procure him the same moral advantage as the condition of his funds after his stake. Whence we draw this conclusion: that the game is disadvantageous, even in the cases where the stake is equal to the product of the sum hoped for by the probability. We may, therefore, form an idea of the immorality of games in which the hoped-for sum is below this product.
Jacques Bernouilli has thus laid down the result of his investigations on the calculation of probabilities. An urn containing white and black balls is placed in front of the spectator, who draws out a ball, ascertaining its colour, and puts it back in the urn. After a sufficient number of draws, the total number of extracted balls divided by the total number of balls represents a fraction very near to that which has for a numerator the real number of white balls existing in the urn, and for the denominator the total number of balls. In other words, the ratios of the number either of extracted white balls, or the whole of the white balls to the total number, tend to become equal; that is, the probability derived from this experiment approaches indefinitely towards a certainty. The two fractions may differ from each other as little as possible, if we increase the number of draws. From this theorem we deduce several consequences.
1. The relations of natural effects are nearly constant when these effects are considered in a great number.
2. In a series of events indefinitely prolonged, the action of regular and constant causes affects that of irregular causes.
Applications.—The combinations presented by these games have been the subject of former researches regarding probabilities. We will complete our exposition with two more examples.
Two persons, A and B, of equal skill, play together on the understanding that whichever beats the other a certain number of times, shall be considered to have won the game, and shall carry off the stakes. After several throws the players agree to give up without finishing the game; and the point then to be settled, is in what manner the money is to be divided between them. This was one of the problems laid before Pascal by the Chevalier de Méré. The shares of the two players should be proportional to their respective probabilities of winning the game. These probabilities depend on the number of points which each player requires to reach the given number. A’s probabilities are determined by starting with the smallest numbers, and observing that the probability equals the unit, when player A does not lose a point. Thus, supposing A loses but one point, his chance is 1·2, 3·4, 7·8, etc., according as B misses one, two, or three points. Supposing A has missed two points, it will be found that his chance is as 1·4, 1·2, 11·6, etc., according as B has missed one, two, or three points, etc. Or we may suppose that A misses three points, and so on.
We should note, en passant, that this solution has been modified by Daniel Bernouilli, by the consideration of the respective fortune of the players, from which he deduces the idea of moral hope. This solution, famous in the history of science, bears the name of the Petersburgh problem, because it was made known for the first time in the “Memoires de l’Académie de Russie.”
We will now describe the game of the needle. It is a genuine mathematical amusement, and its results, indicated by theory, are certainly calculated to excite astonishment. The game of the needle is an application of the different principles we have laid down.
If we trace on a sheet of paper a series of parallel and equi-distant lines, AA1, BB1, CC1, DD1, and throw down on the paper at hazard a perfectly cylindrical needle, a b, the length of which equals half the distance between the parallel lines (figs. 858 and 859), we shall discover this curious result. If we throw down the needle a hundred times, it will come in contact with one of the parallel lines a certain number of times. Dividing the number of attempts with the number of successful throws, we obtain as a quotient a number which approaches nearer the value of the ratio between the circumference and the diameter in proportion as we multiply the number of attempts. This ratio, according to the rules of geometry, is a fixed number, the numerical value of which is 3·1415926. After a hundred throws we generally find the exact value up to the two first figures: 3·1. How can this unexpected result be explained? The application of the calculus of probabilities gives the reason of it. The ratio between the successful throws and the number of attempts, is the probability of this successful throw. The calculation endeavours to estimate this probability by enumerating the possible cases and the favourable events. The enumeration of possible cases exacts the application of the principle of compound probabilities. It will be easily seen that it suffices to consider the chances of the needle falling between two parallel lines, AA1 and BB1 (fig. 858), and then to consider what occurs in the interval, m n, equal to the equi-distance. To obtain a successful throw, it is necessary then:—
1. That the middle of the needle should fall between m and l, the centre of m o. 2. That the angle of the needle with m o will be smaller than the angle, m c b. The calculation of all these probabilities and their combination by multiplication, according to the rules of compound probabilities, gives as the final expression of probability the number.
This curious example justifies the theorem of Bernouilli relating to the multiplication of events; there is no limit to the approximation of the result, when the attempts are sufficiently prolonged. When the length of the needle is not exactly half the distance between the parallel lines, the practical rule of the game is as follows: The ratio between the number of throws and the number of successful attempts must be multiplied by double the ratio between the length of the needle and the distance between the parallel lines. In the case cited above, the double of the latter ratio equals the unit. We will give an application to this. A needle two inches long is thrown 10,000 times on a series of parallel lines, two-and-a-half inches apart; the number of successful throws has been found to equal 5000. We take the ratio 1090/5009, and multiply it by the ratio 1000/636 and the product is 3·1421. The true value is 3·1415. We have an approximation of 6/10000.
The dimensions indicated in this experiment are those which present in a given number of attempts the most chances of obtaining the greatest possible approximation. We will conclude these remarks on games by some observations borrowed from Laplace.
The mind has its illusions like the sense of sight; and just as the sense of touch corrects the latter, reflection and calculation correct the former. The probability founded on an every-day experience, or exaggerated by fear or hope, strikes us as a superior probability, but is only a simple result of calculation.
In a long series of events of the same kind, the mere chances of accident sometimes offer these curious veins of good or bad fortune, which many persons do not hesitate to attribute to a kind of fatality. It often happens in games which depend both on chance and the cleverness of the players, that he who loses, overwhelmed with his want of success, seeks to repair the evil by rash playing, which he would avoid on another occasion; he thus aggravates his own misfortune and prolongs it. It is then, however, that prudence becomes necessary, and that it is desirable to remember that the moral disadvantage attaching to unfavourable chances is increased also by the misfortune itself.[41] Mathematical games, formerly so much studied, have recently obtained a new addition in the form of an interesting game, known as the “Boss” puzzle. It has been introduced from America, and consists of a square box, in which are placed sixteen small wooden dice, each bearing a number (fig. 860). No. 16 is taken away, and the others are placed haphazard in the box, as shown in fig. 861. The point is then to move the dice, one by one, into different positions, so that they are at last arranged in their natural order, from one to fifteen; and this must be accomplished by slipping them from square to square without lifting them from the box. If the sixteenth dice is added, the game may be varied, and we may seek another solution of the problem, by arranging the numbers so that the sum of the horizontal, vertical, and diagonal lines gives the number 34. In this form the puzzle is one of the oldest known. It dates from the time of the primitive Egyptians, and has often been investigated during the last few centuries, belonging, as it does, to the category of famous magic squares, the principles of which we will describe. The following is the definition given by Ozanam, of the Academy of Sciences, at Paris, at the end of the seventeenth century. The term magic square is given to a square divided by several small equal or broken squares, containing terms of progression which are placed in such a manner that all those of one row, either across, from top to bottom, or diagonally, make one and the same sum when they are added, or give the same product when multiplied. It is therefore evident from this definition, that there are two kinds of magic squares, some formed by terms of arithmetical progression, others by terms of geometrical progression. We must also distinguish the equal from the unequal magic squares.
We give here several examples of magic squares with terms of mathematical progression, among them the square of 34, giving one of the solutions to the puzzle just described (fig. 862). We also give an example of a magic square composed of terms of geometrical progression. The double progression for examples 1, 2, 4, 8, 16, 32, 64, 128, 256, as here arranged (fig. 863), forms such a square that the product obtained by multiplying the three terms of one row, or one diagonal, is 4,096, which is the cube of the mean term 16. The squares have been termed magic, because, according to Ozanam, they were held in great veneration by the Pythagoreans. In the time of alchemy and astrology, certain magic squares were dedicated to the seven planets, and engraved on a metal blade which sympathized with the planet. To give an idea of the combinations to which the study of magic squares lends itself, it is sufficient to add that mathematicians have written whole treatises on the subject. Frénicle de Bessy, one of the most eminent calculators of the seventeenth century, consecrated a part of his life to the study of magic squares. He discovered new rules, and found out the means of varying them in a multitude of ways. Thus for the magic square, the root of which is 4, only sixteen different arrangements were known.
Frénicle de Bessy found 880 new solutions. An important work from the pen of this learned mathematician has been published under the title of “Carrés ou Tables Magiques,” in the “Memoirs de l’Académie Royale des Sciences,” from 1666-1699, vol. v. Amateurs, therefore, who are accused of occupying themselves with a useless game, unworthy the attention of serious minds, will do well to bear in mind the works of Frénicle, and better still, to consult them.
We have so far considered only the first part of the puzzle. We may now examine the problem to which specially it has given rise. We are quite in accord with M. Piarron de Mondesir, who has been so good as to enlighten us upon the subject, which is really much more difficult than it appears.
A French paper once proposed to give a prize of 500 francs to any individual who would solve the following problem:—
Throw the numbers out of the box, replace them at hazard, then in arranging them place them in the following order (A fig. 864).
Now nobody solved this problem, because in nine cases out of ten it is impossible to do so. The first twelve numbers will come correctly into their places, and even 13 can be put in its place without much trouble; but, instead of getting the last row right we shall find it will come out like B, viz., 14, 15, 13, in the large majority of instances. So any case can be solved in one of the two results given above, and we can tell in advance, without displacing a number, in which way the puzzle will eventuate.
Let us give this problem our attention for a few minutes, and we shall not find it difficult.
Take the first example. We will throw the cubes out of the box and put them back in the order shown in fig. 865.
We see now that 1 occupies the place of 11, 11 that of 7, 7 that of 8, 8 that of 6, 6 of 15, 15 of 1. This much is evident without any study. We formulate these figures as follows, beginning with 1 and working from figure to figure till we are led to 1 again, and so on.
1st. Series.—1, 11, 7, 8, 6, 15, 1 (6) even.
Counting the number of different cubes we have 6; and we put (6) in a parenthesis. We call the first series even because 6 is an even number.
We now establish, by the same formula, a second series commencing with 2, and going back to it, thus—
2nd Series.—2, 4, 2 (2) even. 3rd Series.—3, 5, 10, 12, 3 (4) even. 4th Series.—9, 13, 14, 9 (3) uneven.
We have now four series, the total number of points equal 15, as there ought to be, for one cube is absent.
Let us now take another example (see fig. 866), and by working as before we have four series again, viz:—
1st Series.—1, 7, 1 (2) even. 2nd Series.—2, 11, 3, 8, 4, 15, 2 (6) even. 3rd Series.—5, 12, 13, 5 (3) uneven. 4th Series.—9, 14, 10, 9 (3) uneven.
This gives us only 14 as a total, because 6 has not been touched at all.
* * * * *
And now for the rule, so that we may be able to ascertain in advance, when we have established our series, whether we shall find our puzzle right or wrong at the end. We must put aside all unplaced numbers and take no notice of uneven series. Only the even series must be regarded.
Thus if we do not find 1, or if we find 2, 4, or 6, the problem will come into A as a result. If we find 1, 3, 5, or 7, the case will eventuate as in B (fig. 864). Let us apply the rule to the problems we have worked, and then the reason will be apparent.
In the first we find three even series; the problem will then end as in B diagram (fig. 864), for the number of like series is odd.
In the second we find two even series (pairs); we shall find our problem work out as in diagram A (fig. 864), for the number of like series is even, one pair in each.
We are now in possession of a simple rule, both rapid and infallible, and which will save considerable trouble, as we can always tell beforehand how our puzzle will come out. Any one can test the practicability of the rules for himself, but we may warn the reader that he will never be able to verify every possible instance, for the possible cases are represented by the following sum—
2×3×4×5×6×7×8×9×10×11×12×13×14×15.
That is to say, 1,307,674,368,000 in all.
SOLITAIRE.
This somewhat ancient amusement is well known, and the apparatus consists of a board with holes to receive pegs or cups to receive the balls, as in the illustrations (figs. 867 and 870.) The usual solitaire board contains thirty-seven pegs or balls, but thirty-three can also be played very well. Many scientific people have made quite a study of the game, and have published papers on the subject. M. Piarron de Mondesir has given two rules which will prove interesting.
The first is called that of equivalents, and supposes the game to be played out to a conclusion; the second, called the ring-game, admits of a calculation being made so that the prospects of success can be gauged beforehand.
The method of play is familiar, so we need not detail it. It is simply “taking” the balls by passing over them in a straight line. The method of “equivalents” consists in replacing one ball with two others, as we will proceed to explain by the diagram (fig. 868).
Suppose we try the 33 game, which consists in filling every hole with the exception of the centre one, and in “taking” all the balls, leaving one solitary in the centre at the last. Suppose an inexperienced player arrives at an impossible solution of five balls in 4, 11, 15, 28, and 30.
To render the problem soluble, and to win his game, I will replace No. 11 by two equivalents, 9 and 10, the ball 28 by two others, 23 and 16, and the ball 30 by 25 and 18. These substitutions will not change the “taking off,” for I can take 10 with 9, 23 with 16, and 25 with 18. But by so doing I substitute for an irreducible solution of five balls a new system of eight (those shown with the line drawn through them in the diagram), which can easily be reduced to the desired conclusion, and the game will be achieved.
There are in reality three terminations possible to the problem—the single ball, the couple, and the tierce; that is, you may have only one left, or two placed diagonally, such as 9-17, 25-29, or a system of three in a straight line, 9-16-23. By the “equivalents” you can always succeed in solving the problem desired.
We will now point out four transformations which are very easy to effect, and result from the rule of “equivalents.”
1. Replacement of the two balls, situated on the same line and separated by an empty cup, by one put into that cup. Thus I can replace 23 and 25 by a single ball at 24.
2. Suppression of tierces. And by the above movement I suppress the tierce 9-16-23.
3. Correspondent “cases” are two holes situated in the same line and separated by two cups. If two corresponding cups are filled, I can suppress the balls which occupy them. So I can put aside 4 and 23.
4. It is permissible to move a ball into one of the correspondent cups if it be vacant; thus I can put 10 into 29.
These are the four transformations which can be made evident with the rings, without displacing the balls. To do this we need have only seven rings large enough to pass over the balls and to surround the holes in which they rest. Let us take an example.
Solitaire with 33 holes (fig. 869). Final solution of the single ball.
1st Vertical row: 7 and 21 are occupied, and the intermediate hole 14, being empty, I place a ring upon 14.
2nd Vertical row: No. 8 takes 15, and comes into 22; I place a ring on 22.
3rd Vertical row: I suppress the corresponding balls, 4-23 and 16-31, there now only remains 9, so I place a ring on 9.
4th Vertical row: I suppress the correspondents 10-29, put 2 into 17, and I place a ring upon 17.
5th Vertical row: I suppress correspondents 6-25, put 33 into 18, and I place a ring upon 18.
6th Vertical row: No. 12 takes 19 and comes to 26; I place a ring on 26.
7th Vertical row: No. 20 is the only ball; I place a ring on 20.
(It must be understood that these operations should be proceeded with mentally; the balls must not be disturbed.)
We have thus reduced the problem to seven ringed balls, which are 14, 22, 9, 17, 18, 26, and 20 which are indicated on the diagram by the line drawn through each vertically. They are all comprised in the three horizontal rows, 3, 4, 5.
We can now set to work upon these three rows in the same manner as before, considering the rings as balls.
3rd row: We find (and leave) a ring upon 9.
4th row: The two corresponding rings, 17-20, neutralize each other, and we suppress them. We carry 14 to 17, and take 17 with 18, which comes into 16. We leave a ring on 16.
5th row: Carry the ring 26 to 23, take 23 with 22, which comes thus to 24, and we leave a ring on 24.
We now have reduced our problem to three rings, 9, 16, and 24, all in the central square, indicated in the diagram by horizontal bars. It is easy to see that 9 will take 16 and 24 and come into 25, and 25 will remain alone—as was intended to be done—a single ball upon the board, indicated by the circle around it in the cut.
By playing the “equivalent” method you will always arrive at this result—a single ball in No. 25. It may now be perceived how we cannot only arrive at a satisfactory solution, but by means of the rings ascertain whether we shall succeed in our game without disturbing a single ball. After some experience we may even learn to dispense with the rings altogether.
FOOTNOTES:
[41] From “La Nature.” Notice of M. Ch. Boutemps.
LVII. THE MAGIC TOP—THE GYROSCOPE AND SCIENTIFIC GAMES
We will not do our readers the injustice to suppose that they are not familiar with the ordinary top,—the delight of all school-boys and young people,—of which, therefore, we forbear giving any description; but we now desire to give some details of the construction of the wonderful magic top. It is composed of a large disc, with an axis turning on two pivots connected with a circle of iron. When in repose, this plaything exhibits nothing of a remarkable character; it is completely inert, obeying, like all other bodies, the laws of gravity. But when we come to give the disc a movement of rapid rotation, this inert instrument seems to assume a vitality of its own if we attempt to move it; it resists, and seems to thrust back the hand, and executes movements even in a contrary direction. Besides this, it appears to be freed, in a certain measure, from the laws of gravity; if we place it on its pivot, instead of falling, as it would when the disc is motionless, it preserves the upright or inclined position in which we place it, the upper extremity of the axis slowly describing a horizontal circle round the fulcrum of the other extremity.
Few persons are sufficiently familiar with the theory of mechanics to understand these phenomena, and it often happens that such a top purchased to amuse a child becomes an object of wonder and interest to his seniors. We do not pretend here to explain mathematically the reason of the facts before us, but the mechanical principle on which this top is constructed is of such great scientific importance, that we will, in a few words, explain it to our readers. It is sufficient to have a little knowledge of mechanics to be aware that a body in motion, subjected to the action of a force tending to give it a directly contrary motion, will follow a movement in a third direction, which is termed the resultant of the two others; and this resultant approaches nearer to one of the original directions, in proportion as the corresponding movement is more rapid in relation to the other. If, for example, you strike a billiard ball, which is rolling past you, in such a manner that you drive it regularly along in the same direction, it appears only to obey a part of the given impulsion, and continues its course in an oblique direction, the speed with which it commenced rolling combining with the impulsion to produce a resultant movement. If it is rolling very quickly, and you strike it gently, it will scarcely turn out of its course. If, on the contrary, it is moving slowly, and receives a violent shock, it will run off almost exactly in the direction in which it has been struck.
Now that which occurs in this example of a body tending to two movements at the same time, is also produced when it is a question of movements of rotation, so that if a force acts upon a body in rotation in such a manner as to give it a movement of the same kind round another axis, a third movement will be originated round a third axis, the direction of which will be nearest to that in which the rotation is most rapid. Let us apply this very simple principle to our top, and we shall see that magic has nothing whatever to do with these movements, which at first glance appears so extraordinary. Having set it in motion, we rest it on its pivot, its axis in a horizontal position; we then find that we have two movements before us; first, that which we gave the top ourselves, and secondly, the movement of rotation which occurs round a second axis equally horizontal passing through the fulcrum and perpendicular line to the first. A movement of rotation therefore originates round a third axis placed between the two first, but whilst the real axis of the top, obeying this resultant movement, takes up its new position, the law of gravity continuing to act, displaces and moves it a little further, so that in endeavouring to reach its centre of gravity, it turns round its fulcrum (fig. 871). From this explanation, it will be easily seen that the more rapid the movement given to the top,—that due to gravity remaining constant,—the nearer will be the axis of the resultant movement to its real axis, and consequently the slower will be the movement of rotation of the whole round the pivot. Thus this apparently incomprehensible phenomenon is easily explained by gravity, vertical force producing a movement of rotation in a horizontal plane. One can also explain by analogous reasoning, and calculation of passive resistance, why the axis of the top gradually inclines in proportion as the speed of the latter diminishes, and the speed of rotation round the fulcrum increases; why it falls immediately if an obstacle is opposed to the latter movement, and finally, why it produces on the hand which holds it, movements which astonish persons so intensely who behold it for the first time.
The principle we have just described is often enunciated, by saying that every body in rapid rotation rests in its plane, and can only be driven out by a considerable force; this, however, is a defective formula. The principle should be stated in the following manner. A body in rapid rotation tends to remain in its plane; that is, its axis rests parallel with itself, and instead of obeying any force tending to divert its direction, it produces in consequence of the combination of two simultaneous movements, a displacement of the axis, generally much feebler and of a different kind from that which this force exercises on the same body in repose. One of the most charming applications of this theory is due to M. Foucault. The Gyroscope, which bears his name, is a heavy disc, the axis of which is supported by a “Cardan” balance, so that, whatever is the position of the contrivance, it is possible to preserve it in a constant direction. Therefore if the disc is, by means of special mechanism, put in rapid rotation, we may give it all kinds of possible displacement without changing the plane in which the gyroscope moves. Supposing then that its connection with the suspension is fixed in a relatively immovable manner, but attracted by a movement towards the ground, the plane of rotation of the disc will not entirely participate in this movement. It is true, it will be carried into the movement of general removal, but it will remain constantly parallel with itself, and only appears displaced in comparison with the surrounding objects, which obey more completely than itself the movement of the globe’s rotation round its poles. Thus can we demonstrate the movement of our planet. In virtue of the same principle, we see every day passing before our eyes a crowd of phenomena with which we are so familiar that they do not excite our attention. Thus it is because the hoop tends to remain in its plane of rotation that it rolls on without falling or deviating, and for the same reason that tops rotate vertically on their points, or when they are running down, describe a series of concentric circles; and for the same reason again, a juggler is able so easily to hold on the point of a stick a plate which he puts in rapid rotation, etc. It is also owing to this property of rotating bodies that we have been enabled to make use of cylindrical or conical projectiles in artillery. The coiled riflings of the cannon causing the projectiles to turn round very rapidly, their axis preserves an invariable direction during their whole course, until they finally strike the object at which they are aimed. Without this rotation they would pirouette in an irregular manner in the air, and besides any precision in firing being impossible, the resistance of the air would diminish their range to an enormous extent.
The Gyroscope, an instrument now familiar to most scientific persons, is still a problem of which the solution has not yet been found. It may be called the paradox of mechanics, for although it depends on gravitation, it appears to be entirely indifferent to it.
An American scientist has applied electricity to the gyroscope, so as to make its movements as continuous as possible, and to enable us to study it more at leisure and with better results. The gyroscope is mounted on a pedestal which tapers to a point, and supports the instrument. The bar of the gyroscope on which the electro-magnets are fixed rests upon the top of the pedestal. One of the extremities of the bobbin is fixed to the cavity, when the bar and support join, the other extremity communicates with the bar which joins the nuts of the magnets.
An insulator of hardened caoutchouc is so placed that it just touches the axis of the wheel twice in every revolution of that wheel. Its plane of rotation is at right angles to the magnets, and carries an armature of soft iron which turns very close to the magnet without touching it. The armature is put en rapport with the surface of contact of the cylinder, so that when the armature approaches it is attracted; but immediately afterwards, as it reaches the opposite side, the current is interrupted, and the impulse acquired is sufficient to move the wheel to the spot where the armature can again come under the influence of the magnet.
The magnets, the wheel, and all the parts of the instrument together can move around in any direction. When two or four Bunsen cells are put in connection with the gyroscope, the wheel turns with tremendous rapidity, and by permitting the magnets to work (an operation which requires some little dexterity), the wheel not only sustains itself, but also the magnets and the other subjects which are between it and the extremity of the pedestal—in opposition to the laws of gravitation. The wheel, besides turning rapidly around its axis; revolves slowly around the point of the column in the same direction taken by the lower part of the wheel.
When attaching the arms and counter-poise of the machine, so that the wheel and the magnets may balance themselves exactly on the pointed pedestal, the machine remains stationary. But if we give any preponderance to the wheel and magnets the rotation of the apparatus is in a direction opposite to that which would result from turning the upper part of the wheel.
The gyroscope illustrates the persistence with which a body that submits to rotation maintains itself in the plane of its rotation, notwithstanding the force of gravitation. It also shows the result of the combined action of two forces tending to produce rotation around two separate axes, which are, however, situated in the same plane.
The rotation of the wheel round its axis is produced in the present case by the electro-magnet; and the tendency of the wheel to fall, or to turn in a vertical plane parallel to its axis, results in the rotation of the entire instrument upon a new axis, which coincides with the pointed pedestal.
THE AMERICAN MONEY-BOX.
During a recent visit to London, as I was one day walking in the Crystal Palace, my attention was attracted by a curious money-box, surmounted by a pictorial representation of one of the London streets. The carriages, horses, and pedestrians were represented by figures cut out of cardboard, arranged in a groove. A large placard bore this inscription: “Notice to visitors: Throw a penny in the money-box; and the figures will perform.”
I at once responded to this invitation, and immediately beheld the little tableaux become moving and life-like; the cabs rolled along, and the passers-by walked up and down the street. A number of visitors followed my example, and there is no doubt the money-box was full at the end of the day. This ingenious contrivance for obtaining money in so easy a manner, and without having recourse to a “show-man,” appeared to me worthy of investigation and description.
The Scientific American (New York) has recently given an explanation of this curious contrivance, and we will here quote what has been published on the subject.
“Among the inventions intended to obtain contributions of money from the visitors at the Philadelphia Exhibition,” says the American writer, “we will describe the singular money-boxes placed in the salons of the principal hotels and the galleries of the exhibition, etc. These contrivances all consisted of a case or box, with a glass front, through which can be seen a landscape in miniature, with trees, houses, figures, etc., all cut out of cardboard, and painted with great nicety. On the box was a label requesting the visitor to drop a coin into it and await the result of the contribution. When the penny has fallen in it puts in motion some hidden machinery, and then we see the people in the miniature landscape all in motion, riding or walking or hunting, as the case may be.”
Another box is even more successful, for it places in the hands of the contributor a photograph of some celebrated person. But to obtain the photograph we must contribute six pennies. The carte will not come out if we do not put in the proper coins, and the apparatus is perfectly fair and honest.
The illustration, fig. 872, shows the apparatus, which is very simple. On the left the ordinary box is seen, on the right there is a longitudinal section of it.
At the top of the lower portion, where the money is received in, is a hollow support, A, which sustains the box in which the photographs are placed upon an inclined plane, and resting against the glass. The pieces of money, in falling, strike the extremity of a vertical balance, which immediately turns a toothed wheel, C. This wheel has as many teeth as there are pieces of money necessary to purchase the photograph or carte de visite. Upon the escapement wheel is a ratchet arrangement, D, the shaft being moved by a cord rolled around it and attached to a spring, E. A bolt, F, moved by a spring, is kept constantly pressed against the “snail,” D.
Thus at each revolution, as the parts of the machinery are animated by the same movement, the bolt is withdrawn sufficiently to permit a carte to fall, and then the card next following will be ready resting upon the bolt. The photographs being placed upon an inclined plane, are pushed forward by a movable frame, G, which has a roller at the base. So as one card falls out another is immediately replaced close to the glass.
We have remarked that the wheel has six teeth, so that as one piece of money dropped in moves it one-sixth of its revolution, six pieces will be necessary to produce the card. Of course wheels can be made with one or more teeth, and the payment may be varied for valuable objects at the desire of the possessor.
The invention is not only a plaything. It can be made useful in the distribution of pamphlets, or newspapers, which can be introduced into the box folded uniformly. They can also be used in omnibuses or tram-cars, and tickets may be given by the machine on payment of the proper sum of money.
We will close this chapter with an illustration of a spiral bottle, which can be done in the manner now to be described, so that the bottle will actually become a glass spring.
Take a mixture of 180 grammes of lampblack, 60 grammes of gum arabic, 23 grammes of adraganth, and 23 grammes of benzoin. Make these ingredients into a paste by the addition of water, and fashion a pencil of the charcoal thus obtained. This pencil, when heated, will cut the glass wherever it is applied.
The process is commenced by scraping the bottle with a file and following the instrument with the red-hot pencil. Wherever the hot pencil is applied, the glass will be cut as shown in the illustration herewith. It will be necessary to blow upon the heated pencil to maintain the incandescence as long as possible. The bottle as cut and representations of the instruments are given in the cut (fig. 873).